I reduced to one card to test overclocking. The first card manage to get to 675 core, 1125 memory. The memory appears to jump in 25mhz increments, while the GPU goes at 5mhz jumps (CCC wont let me go less than 5mhz per jump on the core). The means the 4850 doesnt really run at 993 memory, it runs at 975. Or at least thats what GPU-Z says. So, I managed to squeeze 50mhz out of both the core and the memory.
4850 Single Card, Default Speeds, POST Hotfix
Crysis = 28.46
3D06 = 12624 (SM2 = 4774, SM3 = 5731)
4850 Single Card, Overclocked to 675/1025 Post-Hotfix
Crysis = 30.11
3d06 = 13196 (SM2 = 4997, SM3 = 6017)
Roughly 5% more speed.
I cant do a overclock crossfire test until a rivatuner version becomes available, or the radeon bios editor is safe to change the clocks.