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 :(

I found the problem, its summer (here) so my imac can overheat easier, i decided to put a fan behind my comp :P. Now i get constant 100 fps :)
By the way, THANKS to everyone that gave me advices, you guys are awesome

yeah, my mac gets really high temperature, when i play tf2, gets 67-70 ºC (152.6-158ºF)

still having low fps, comanglia's config is better but the fps are almost the same :( Any reason why did the fps went down in 2 years?

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 mac:
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 :(