2 5830 if your PSU is at least 600w.
downclock the memory to lower power use.
2x5830 = 500-600 Mh
1x 5850 = 300-400 Mh
I picked up my 5830's for $80 a pop. Look around, 5850's are over $200.
i got a 650Watt PSU
I already got a 5850 in there.
5850 use about 250 if im not mistaken.
How much power does a 5830 use?