I am creating this thread to better consolidate this topic from various other posts. I have probably mucked up some other threads and gone off topic, so I feel it better to try and stay on point at least somewhere.
In short, I am experiencing substantially lower performance in OS X than Windows 7 when using 7xxx cards. The issue does not appear to be limited to the 7950 as I have also tested a 270X. The problem seems to only plague the MP 3.1 as others are experiencing much better results on other model Mac Pros. I have seen links to results on 2.1 and 1.1 models that surpass my own. Blacksheep and others have demonstrated the 7xxx cards are capable of coming close to, if not matching, Windows performance in OS X. The argument has been made that the MP3.1 is hardware limited when compared to the 4.1 or 5.1, but hardware limitations should result in similar limits across any OS. It also wouldn't explain how even older models from 2006 or 2007 can surpass the 2008. I have attached various screen grabs showing the disparity.
I have performed a completely fresh install of OS X, removed APGM (replaced after no change seen), and tested 10.9.2 beta 1. In all I have used 10.8.4, all 10.8.5 betas and final, every DP of Mavericks, 10.9.0, 10.9.1 betas and final, and 10.9.2 beta 1. I have tried both Sapphire 7950 Mac Edition and an XFX 270X. I have used stock bios, OC'd bios, EFI and non-EFI bios... the situation stays the same. The 7950 Mac performed this way out of the box in EFI and Windows settings. I don't believe it is defective cards as this now effects three different GPU's from different series lines. The diminishment is nearly the same percent between the 270X and 7950's. I don't know if the cards are throttling in OS X, but they aren't in Windows, nor should they be. LuxMark results remain constant from start to end of testing, so there doesn't appear to be any degradation after loading. The TDP limits on the 7950's have been raised and I have a secondary 750W PSU pushing the GPU's PCIe 4 x 6-pin power inputs. The system is rock solid stable in Win7 under various torture tests and the GPU's never throttle down. I own two different Mac Pro's from 2008 and have tested all three cards in both machines. Results are consistent. The problem does not appear to be isolated to one framework like OpenCL or OpenGL alone.
LuxMark Sala Scene (OpenCL):
XFX 270X: Stock OS X - 870; Stock Win 7 x64 - 1606. 54.2% OS X output vs Win7.
2 x 7950 OC: OS X - 2857; Win 7 x64 - 4732. 60.4% OS X output vs Win7.
Heaven Basic Preset Benchmark (OpenGL):
7950 OC: OS X - 62.8 fps, 1582 score; Win 7 x64 - 103 fps, 2595 score. 60.1% OS X output vs Win7.
Heaven Extreme Preset Benchmark (OpenGL):
7950 OC: OS X - 22.8 fps, 575 score; Win 7 x64 - 46 fps, 1159 score. 49.6% OS X output vs Win7.
Stock 7950 tested by Barefeats: 38.7 fps -
http://www.barefeats.com/gpu7950.html. 58.9% vs Barefeats.
Valley Basic Preset Benchmark (OpenGL):
7950 OC: OS X - 41.3 fps, 1728 score; Win 7 x64 - 32 bit only
Valley Extreme Preset Benchmark (OpenGL):
7950 OC: OS X - 29 fps, 1213 score; Win 7 x64 - 32 bit only
Stock 7950 tested by Barefeats: 33.1 fps -
http://www.barefeats.com/tube04.htmlValley Extreme HD Preset Benchmark (OpenGL):
7950 OC: OS X - 22.8 fps, 952 score; Win 7 x64 - 32 bit only
OceanWave (OpenCL):
7950 OC: OS X- 506.8 fps; Barefeats - 548 fps -
http://www.barefeats.com/gpu7950.html5770: OS X- 146.3 fps; Barefeats - 138 fps
270X: OS X- 353.9 fps; Barefeats - Not Tested
Luxmark Sala Scene with single stock 7950 Mac Edition on Mac Pro 3,1:
10.8.3 - 1449
10.8.5 - 1442
10.9.2 - 1242
10.9.3 13D12 - 1287
Win7 - 1792