Thanks for the replies guys. Lots of good info here.
I hadnt actually thought about
1. flashing the bios
2. setting clock speeds
Is it the case that in essence the rig should work as is albeit not at the best efficiencies and that points 1 & 2 above are best executed once the rig is fully tested and then needs to be optimized?
Thanks!!
All cards will be able to attain the maximum efficiency possible for every card, mixing has nothing to do with it.
There's also not much testing to do, if they boot then they work. After that just mod/flash the BIOSes, being careful not to flash a BIOS on the wrong card, though you can easily recover it since you have multiple cards.