My Linux gaming experience has been a bit sub par since upgrading to a Radeon R9-380.
It was just laggy enough to make playing hard. You often don't see the person that's killed you and things like air blasting rockets in TF2 was almost impossible to time right.
However things seems to have turned. With Kernel 4.5, the amdgpu driver and adding the amdgpu.powerplay=1 to your kernel options in GRUB speed of gaming and even YouTube is quite noticeably improved.
The other problem I had been having was TF2 would freeze after a few games and you had to do the old alt prt-sc REISUB to reboot. Touch wood that also seems to be fixed.
So a big debt of thanks to the Kernel team and particular the amdgpu guys.