I initially had a problem with the GPU. I have since replaced the GPU and had a working iMac again! For like 3 days, then the...
I bought my 5670 on Gainsaver and it did not work for me at all. I can't verify whether it was a faulty GPU or that it just wasn't compatible. There was no boot chime or anything, I even tried a new power supply. I ended up ordering another radeon 4670 and it ended up working fine... for a few days. then it kind of crapped out on me. I can still boot and I think it actually loads up fine, because when I hit the volume, I could hear the clicks! I'm hoping I just !@#$%^ up the display connector from disconnecting and reconnecting so many times. I ordered the part, but the only place I could find it was some guy in china, so I've been waiting on it for a week or two now. If it doesn't work, I've about had it with this thing, and will probably end up just backing up the harddrive and parting it out.
I'm going to assume since Thomas never responded, that it worked and he never had a problem again. I I ordered the 5760, because it was an option on my generation iMac, and Mac anywhere shoes them having the same chipset. My only concern is with the heat and power requirements. I have the mid 2010 iMac, generation 11,2 with 4760, 3.06ghz dual and r4 gigs of ram. Since I've got it open, I'm going to replace the VRAM battery and upgrade my memory by adding 2 4 gb memory sticks for a total of 12 gb. I'm going to leave the 500 gig hard drive.