up to 450MHash/s on 2 x 6770 when I push em hard.  When I can't babysit em, it goes down to about 395MHash/s but then I throw my laptop in to cover some of the difference (it does 44Mhash/s on a first generation A8 APU).  Just ordered two more gigabyte 6770s @ $107 each via TigerDirect.  Get em on Tuesday. 

Also have 4 riser cables coming in (2 x PCIe x1 to PCIe x16 cables and 2 x PCIe x16 extender cables).  Check amazon if interested.  These seem to be neccessary if running more than two cards, even on a ATX board.