I used the BIOS editor from Guru3D to make my own BIOS. I found my 5850s were ok up to about 875/1200 at stock voltage. Right now I believe I have them running at 960/1200 with 1.15V also on my "custom" BIOS.
As for 2D clocks, 157/300 is the default idle clock to save power. 400/900 is considered the "unified video decoder" speed but also with crossfire that's what the 2nd card wants to always idle at (which I believe addresses some screen flashing issues). If you're not having issues I'd leave it.