That GPU will easily fit. An atx case will fit any GPU as long as you don't get low profile. Do you ever plan on crossfiring two 6870's? If you don't you are fine with that PSU. My bro runs 2 6950's with a 600w. If you ever do want to crossfire then I would suggest getting a 650w and a different motherboard. Your motherboard only has on PCIe slot. But if you wanna stick with just one GPU you're fine.