So I combined a couple of separate systems into one running in a milk crate last night.

The mobo is from a C2D HP Workstation with 2 PCI-E x16, 1 X8, and 2 X1.

I've currently got to MSI 7870's and a XFX 7850.

I had the 7870's pushing ~475 mh/s ea and the 7850 ~320 OC'd in separate computers.  I wanted to reduce my overhead and test a new setup with risers and such (a proper mining rig).

Now the problem is that I can't seem to overclock them with either Afterburner or Catalyst anymore.  This cuts my production by about ~200 mh/s spread over the three cards.

So the question goes, how do you guys overclock different cards in the same system?  Should I just replace the 7850 with another 7870 and be done with it?

Thanks for the advice- and sorry if it's too much of a NOOB question, I'm starting to figure all of this out.