Thanks for the benchmarks Termie!
Your avg overclocking is mostly the result of the reference card. If you wanted a higher chance of getting into
1250-1320mhz range GPU Boost, it would have been preferable to buy the Galaxy Dual Fan, Gigabyte Windforce 3X or Asus Direct CUII. All 3 of those cards have higher overclocking potential than reference from just about all reviews I've read.
Actually your results are more or less what's expected in the games you tested. HD5850 @ 850mhz has been shown at Xbitlabs to be just
2-3% behind HD5870 at 850mhz GPU clocks.
You have 2 of those in CF ~ 2x HD5870 in CF. Avg frames for HD5870 CF are very close to GTX670 in BF3:
Out of curiosity, can you run BF3 benchmarks again with Ultra settings / 4xMSAA? 4xMSAA was a weakness of HD5800 and HD6800/6900 series in deferred MSAA engines. I am curious to see what happens if BF3 is tested at Ultra with 4xMSAA and how that affects minimum framerates for your 5850 CF setup.
Also, if you test games with tessellation, GTX670 should look much better since HD5800 series has very weak tessellation unit. Games such as Crysis 2, Batman AC and Civilization V would expose that.