Ok, before the gun mettle update i had 60 constant fps with high textures and viewmodels, but when the gun mettle update came out, my fps are 20 even with no-hats and m0res highframes, with that configs I should get +300fps.
About my imac:
I use OS X Yosemite version 10.10.
iMac (21.5-inch, Late 2012 1920 x 1080)
Processor: 2.7 GHz Intel Core i5.
Memory: 8 GB 1600 MHz DDR3.
Graphics: NVIDIA GeForce GT 640M 512 MB.
1 TB of Storage.
8gb of memory.
help :(
exactly the same problem but it is because of the crappy macs, 300+ fps is kinds unrealistic for a mac unless it is modified tbh.
Some things you could try are resetting your pram and smc just in case, as well as installing bootcamp. Once you got bootcamp, run dx8. This removes skins which do greatly affect your fps. osx runs opengl which basically means it's forced to dx9 but if you install bootcamp you can use dx8 as well. These will only help to an extent however because macs really do not have a lot of support for gaming
Also m0res configs are really outdated, I'd recommend getting comanglias toaster fps config here: https://teamfortress.tv/thread/25328/comanglia-s-config-fps-guide