Hackintosh SMBIOS and GPU Performance

[Tyranicus]

I've been having some GPU issues with my hackintosh, and I'm hoping some of the hack gurus on this forum can help me. I have a GTX 470 GPU, and I have read that using the Mac Pro 3,1 SMBIOS does not provide proper power management for this card. However, if I use the Mac Pro 5,1 SMBIOS, I get terrible graphics performance. I am able to play Diablo 3 on the highest settings with 3,1, but it barely runs at the lowest settings on 5,1. Can someone with more knowledge give me some pointers? Ideally, I would like to have decent power management as well as good GPU performance in games.