1 non-OCed 5850 takes 170 Watt.
Keep in mind that 75 Watt will come out of the Motherboard. With 6 cards on the MoBo, I recommend donating the MoBo to me where I will treat it more nicely than you obvioulsy are planning to.
I'll probably use the molex connector adapter from cablesaurus, to avoid damaging the motherboard.
So 170 - 75 = 95
Doesn't each 6 pin give 75 watts though?
Is it 95*6 = 570 or 150*6 = 900? I'm thinking the latter. So I guess another 400 watt power would be enough.