I think they both support crossfire configurations.
Most people here don't have crossfire though, just a bunch of video cards.
I tried that afterburner tweak and it didn't work for me. Maybe I did something wrong... It has the clock capped at 875 for my 5830's. The one I have OC'd w\ trixx shows up as 980 but when i switch to my other 5830 it shows 875 and won't change.
it definitely works
you need to copy the EULA in as well, 2 lines, i just copy-pasted over it entirely