MSI Radeon R7 370 GAMING 4G
To no real surprise, the Radeon R7 370 is certainly playable at 2560x for one of the most popular Linux games: Counter-Strike: Global Offensive. It's playable and the results could be made even better for CS:GO by making this change on Catalyst 15.7.
In part due to Catalyst Linux driver limitations, the Metro Last Light Redux performance is rather low -- just not for the R7 370 but all the AMD GPUs.
The R7 370 comes in slower than the R9 285, but the MSI Radeon R7 370 GAMING 4G costs around $180 while the R9 285 Tonga costs ~$220+.