Ok let's start with this and work our way up or down.
960 Evo SATA prices are bugged but you get the idea.
https://uk.pcpartpicker.com/list/WyYQ6s
Larger SSD/HDD?
More RAM?
More cores?
I'm pretty sure even this GPU is massive overkill for L4D2, don't you need like a 5770 to get 60 fps?

For you this is about how much of an fps increase you're looking for. If everything is fine as it is then the cheapest and best upgrade is no upgrade.

Enable hardware acceleration, if you're doing CPU decoding in the browser you're doing it wrong. If GPU decoding causes high CPU usage then you're doing it very wrong.

If you want overclocking then with your 500£ budget it's 6C/6T i5-8600K + 16GB RAM or 6C/12T i7-8700K + 8GB or any AMD 8C/16T + 16GB RAM (or more).

Software meaning windows or anything else?
When is he going to build it?

150 fps in 6v6 on what settings? Or how many fps are you getting with the 2500K and at what clockrate?
Overclocking will cost you especially on Intel so it's not worth for "longevity" if you could buy a new CPU for the price difference that gets you the same speedup by the time you actually do overclock it.

It won't damage the CPU but at >90°C it'll throttle so any OC that raises the temperature above 90°C will actually cause a slowdown.

Either your fan control is horribly broken or the H60 is horribly broken or incorrectly installed. Games are a light workload compared to some more FPU intensive stuff so 95°C in games is legitimately terrible.

If they are not overclocked.
Which is why it makes absolutely no sense to buy an 8600K or 8350K + Z mobo + cooler (~80-100$) if you're not going to overclock it. 8700 or 8600 + B/H mobo + stock cooler would be faster and cheaper.

So either pay for overclocking and do it or don't and don't (because you can't).

CPUs will boost when needed, that is kind of the whole point. If they boosted a core when it's idle and clocked it down when is use it would be pointless.
You might not get the full single core turbo frequency because multiple cores will be active. Also depending on mobo settings TDP limit might throttle it back down closer to the base clock.

The i5s in general? That's not how it works. Better in what regard? In performance? Obviously not if we're ignoring the 8700T. In price to performance? They all suck compared to the i3s.

Especially the 8400 is pointless for TF2. It's not faster than an i3-8350K on stock clocks and it's not cheaper either.

#2876
No, no difference in TF2.
Also no difference between oc'd 8350K and oc'd 8600K.

The CX450M is actually good and often on sale, the CX450 (2017) is red flag city.
-No reviews mean no review samples. No review samples for a budget PSU means it's shit and they know it.
-Dual sourced. So it's actually two different PSUs. Welcome to the bait and switch.
-They were supposed to be 80+ Silver. Now they're Bronze. The design(s) is (are) significantly worse than expected but they're selling it anyway.
-Apparently it's Half-Bridge LLC. That usually gets you Gold, if not Platinum. This failed Silver. That design is either terribly fucked up or bottom of the barrel components.

Exactly.

Yes.

No, just stick with the stock cooler. If you really want to replace it you can still do that later.

#2868
The question is what do you get out of it?
If you run a game and before you got 64 fps and now you get 72 fps was that worth investing 200 pounds?

Or 8350K on Z170 for the lulz. It's the same die as the 7700K, just needs a BIOS "fix".

If you get an actual M.2 NVMe SSD and not just an M.2 SATA SSD then that would probably faster but also more expensive.

#2869
1. No. What good would the stock cooler be if it couldn't handle the slowest i5 at stock settings?
The stuttering might not be due to the CPU. Both CPU and GPU usage drop massively, something might be interfering.

2. Also you shouldn't use 100% of an SSD's capacity or it'll slow down quite a bit. 120GB SSDs are rarely much cheaper than 240/250GB. For that model it's 20$.

Which "more visible upgrade path" are you talking about?

The RAM might be cheaper if you wait for Zen2/ice/tiger lake but I wouldn't really count that because there's to many variables involved. 8GB and upgrading later is also an option.
Anyway it's more important to know why you're upgrading and whether or not the 6700 is worth it for that.
Zeffy patch would apply to kaby/coffee/ice/tiger lake and Zen/Zen+/Zen2.

If you can sell it. You'd not be limited to the 6700K though.

RAID0 with 2 or 4 SSDs? And why?

#2863
A better thermal paste would buy you maybe 1°C.
Is this even a thermal problem?
If it is only delidding or a better cooler can save you.
If it isn't then you're doing something very wrong because the 8700K boosts to 4.7 GHz.

#2864
The 6700 should be a bit faster. Mostly in multi-threaded but in some single-threaded programs as well.
So what should the upgrade improve and by how much?
A new CPU would definitely be a bigger upgrade but I'm not sure how much you'd have to pay extra.

Just in case: Do you know about the Zeffy patch? https://github.com/zeffy/wufuc Because the glorious overlords at microsoft have decided that no one should get any updates for W7/8 at all if they dare upgrading their hardware without buying W10.

RAID 0, 1 or 5? And why?

If it's still a paste and not dried up it's fine. Depending on the paste it can't even dry up.

So you can use to reapply the thermal paste on an old cooler.
A new cooler should come with new thermal paste or even preapplied paste so using that will obviously be better.

Ok then you'd need ~4.5 GHz (or higher) Skylake assuming the 6700HQ was running at base clock and not throttling. Sustained turbo seems unlikely.
If you've been streaming with NVENC/QuickSync that means i3-8350K + OC (7350K would be an option but would have to be clocked higher and that's cutting it a bit too close), with x264 the extra threads would actually matter so probably an i5-8600K.

https://pcpartpicker.com/list/sxdPnH
This isn't the absolute minimum but the tradeoffs aren't really worth it to save 100$ on a 1100$ build.

#2856
CPU architectures are kind of my thing so I'd be looking at benchmarks anyway. GPUs are not that complicated (in terms of tradeoffs, there is a strict order at least within each manufacturer in terms of speed) and I keep track of that for the technical details as well.
Mobos are easy, RAM is easy, SSD/HDD market doesn't move that fast so basically no work there.
Cases are usually placeholders or just whatever is not shit (dust filters, 2 fans, layout not complete aids) and cheap atm.
PSUs are interesting so I'm reading reviews on new platforms anyway and since 90% are shit or overpriced anyway I just need to look up which PSUs use one of the 2 or 3 platforms worth buying in that performance/price segment and then see if any of those are available or even on sale.

Maybe I'll actually finish the guide before this summer.

#2857
Ok, I'm not entirely sure what the absolute minimum would be. Pub/HL/6s obviously also makes a difference as does minimum vs average vs 95/99 percentile fps.
Tell me how many fps you're currently getting with those settings with which CPU then I should be able to make an educated guess what you'd need.

About the monitor: Are you going for one 24.5" 1080p 240 Hz LCDs or a CRT?

Used parts or everything new?

#2853
A rapsberry pi and any 240 Hz monitor should work.
It won't run many games at 240 fps, but it would run 240 Hz.

A build that will run any game at >240 fps on any resolution and settings isn't possible.
So you'll have to be a bit more specific with your minimum requirements, unless the raspberry pi build is good enough.

#2854
Should be doable. New mobos/chipsets for Intel and new CPUs from AMD are coming so I'd rather not make a partlist now since it'll change quite a bit until next month.
Post again in the week in which you'll buy/build it.

Do it, that'll tell you more than anyone on this forum can.

I'd guess it's the GPU. If the power actually cut out (PSU) the fans couldn't spin up. Mobo issue should cause a power cycle/complete shutdown. Of course it could be a weird PSU/GPU interaction with the PSU actually at fault, or the same with the mobo.

If it still happens with both a different GPU and PSU it's obviously either the mobo, RAM or CPU, but most likely mobo.
Testing the spare GPU first will be the easiest but be careful, if the spare uses less power then just because it's working with the spare doesn't mean it's the GPU's fault. It might still be the PSU so test old GPU + spare PSU as well, just to be sure.