Scrypt Farm Graphics Card Question

[tysat]

Radeon 280X 3GB: $365 Gigabyte GV-R928XOC-3GD REV2
Radeon 7970 3GB: $385 XFX-797AD

Which one should I buy 10-30 of to use for building out a mining farm?  And any suggestions for 3 or 4 cards per rig, and what size PSU to use?

[Equate]

you can buy Radeon 280X 3GB: $365 Gigabyte GV-R928XOC-3GD REV2 as it has better hash rate than 7970 and easy to overclock.For 4 cards 1500watt PSU is sufficient.You need to use risers if you are using 4 cards in single rig in order to keep the temps with in limits.