I'm running 2 5850s in CrossfireX and have the top-rated card performance listed on the mining hardware comparison wiki page (710 MH/s combined). Both run at 99% load. Fwiw. Win7 x64
I would attribute your higher output entirely to your ~200mhz core overclock. What do they put out individually? Have you tried not running them in crossfire for comparison?
Roughly 355 MH/s each with CFX disabled. The GPUs can become very inefficient if the "-f" parameter is set very low (<40). I think this is what's happening in most peoples' cases when they're running CFX.
That's weird, considering I see the exact opposite opposite results when I lower -f. If i set it at 1 the computer becomes hard to use due to graphical lag, but I get an extra ~10% Mh/s.
What if you we're to run the cards independently with -f set to 1?