I still don't get it tbh. Have you even tried the drivers ATI supplies you, the 13 december drivers?
http://support.amd.com/us/gpudownload/l ... ng=English
Now you wanna buy even a second graphics card, while you spent your money already on that ati card, to run you Minecraft?
This all while most games don't even run easily on linux.
Sounds to me like you have too much money, or you're making some weird choices I really don't understand. Anyway, buy the NVIDIA and send me the ati card, I'd like an upgrade
*edit*
So how's my upgrade coming? Bought that nvidia card yet?