yeah the gpu of the 5870 is mire powerful than a gpu of the 5970, but as at the moment hwbot doesn t support multi mixed gpu the rule is to submite with X x best card. X is the number of physical graphic cards.
And here the best card is the 5970.
But yeah logically he can submite as 3 x 5870 but the 5870 has to be the main card(the card plugged to the monitor). For a 3 x GPU result.
Now I dont know if it perform better than 3 physical 5870, if no maybe he can, if yes NO.
Now we have to wait for Massman advice.
And BTW, does ATI drivers support those cards mixed in crossfire ? I have a blackout