I've been in bitcoin for a few weeks now, and I've just been using my HD5850 (OC - 330MHash/s). Now that the difficulty has increase, I've decided to purchase a few more gfx cards. Looking around, the 5850's do well in terms of $ per MHash/s but I have come across a fairly cheap source of some ATI HD6770's.

What MHash/s can I expect from this card? Or would it be better to get another (or 2) HD5850's?

Thanks,