My impression from a logical point of view is a higher dpi sensor scans the surface in a different way, maybe even down to more imperfections in the surface. Like a more detailed magnifying glass.

Other times the sensor (depending onthe mouse) may not be set at a certain dpi in the software but it may not be the "true" accurate dpi

Yeah I have Razer Abyssus, and I don't have any software where I could manipulate the DPI, so there's DPI button under the mouse so yeah I guess it could be inaccurate, there's 450, 1800 & 3500 DPI.

http://www.mouse-sensitivity.com/dpianalyzer.html

Once again not claiming to fully understand the mysteries of the holy mouse, but give this a shot and see how your dpi matches up per IRL distance.

http://www.notalent.org/sensitivity/sensitivity.htm

I'm almost convinced lower DPI means 'slower' movement in general, as less surface is registered during movement.

450DPI may not be natively supported by your sensor even if it allows you to set it? (meaning it's doing some weird extra interpolation to give you that small of a DPI increment) Which mouse do you have?

I just recently did this: I got a new mouse, with a sensor i can change to 2 times what i was use too.
I like 1inch per 360 when I play soldier, my main.

I had Windows at 7/11 mouse sens, and tf2 at 5.6 sens on a 2000dpi set mouse. This equals 1 inch per 360.

I got a new mouse. I set it to 4000dpi, lowered windows to 6/11 (default) and put tf2 at 4 sensitivity. It still equals 1 inch per 360, but my hardware (my mouse) is set to a higher definition. So what i ended up experiencing is a smoother, more responsive mouse, that has the same sensitivity as I am use to.

tldr: DPI is how well your mouse reads movement. Run your hardware as high as you can and adjust the software to maintain your desired, comfortable inches per 360. Control the "sensitivity" using tf2 and or windows. This will allow your mouse to do its job: translate hand movement into in-game head movement, with a higher degree of accuracy.

Please take it easy on him he is new here.

Damn son!

just use the native dpi on your mouse

optical and laser mice use hardware tricks that makes the software think it can go above the native DPI, which makes an optical mouse extremly inaccurate and a laser very inconsistent in acceleration which is the problem OP's having because he's used to the weird inaccuracy of the mouse, so please don't do this, just go with native DPI

if you want to know more about the hardware trick watch this for ~3 minutes https://youtu.be/lc7JVjcPzL0?t=1m29s and you'll find out it's completly bullshit and impossible to raise DPI while maintaining performance

jesus christ how horrifying

I am not saying you should run your mouse at 12000 dpi. This will "raise the noise floor." I am saying run it as high as you can handle. What ever you are comfy with, then turn down tf2 sensitivity until you get the feeling you like. I am saying to go with 1000dpi and 3 in game, rather than 6 in game and 500dpi. Your mouse will read movement better at a higher dpi.

I have done my own tests, and discovered that the mouse feels more responsive and "raw" when choosing a higher dpi, but using the same in/360 by adjusting the software down (the game) instead of the hardware (the mouse).

The reason OP is saying his mouse feels slower, is because his mouse is reading movement (tracking) worst at 450dpi than at 1800dpi.

Some mice are bad and smooth out the signal or have lower malfunction speeds when you use a higher DPI.

What mouse are you using? The DA 3g and 3.5g work best at 1800dpi, so if that's what you're having trouble with, maybe you have mouse acceleration enabled somewhere?

its logical that you have negative accel from using 450 dpi. I had the same when i had MWO (400 DPI)
You can fix this by making your DPI higher or increasing the default polling rate, default 125 Hz, to 500 or even 1000 if your sensor is good
Here is a very easy guide on how to do it
Keep in mind that your sensitivity will be slightly higher if you increase the polling rate

Do you guys just get this information from your own personal experiences? The way you think it feels? If anything, the higher your dpi and the lower your sensitivity, the more prone you are to negative acceleration. The 1800 dpi equivalent of your sensitivity feeling more responsive could only be explained by that DPI step being your mouse's native step. Some mice have a lot of latency on their non-native dpi steps, much like the original ec1/ec2 (evo included) which suffered from massive latency on the 450 dpi step.

Most of the time, if you run a lower sensitivity and a higher dpi, it'll feel more sluggish than if you ran the same sensitivity at a lower dpi.

Generally speaking, 400/450 dpi, a normal sensitivity, and 6/11 windows will grant you the most 1:1 out of game to in game movement.

the negative accel thing is only if you have raw input off. dpi or cpi is only a measure of how many pixels your mouse moves in windows for an irl movement of one inch.

if your mouse has a specific native dpi step, stick with that. if it performs similarly at all steps (pmw3310 for example) anything within the lower half of the available dpi steps should be absolutely fine (most popular mice have some very iffy steps added at the upper end for marketing purposes).

no mouse will perform exactly the same at every step though. mouse movement goes through a bunch of things before being translated to aiming ingame so there is usually a discrepancy in feeling between two theoretically identical sens/dpi combinations. use whatever feels more consistent and predictable to you :)

He has the odd behavior with lower DPI, not higher DPI

not really. you can have negative accel with raw input and i dont think its affected by it
https://www.youtube.com/watch?v=rgbWWTanmQk