What PSU are you talking about for 150usd that will power 4x5970 safely?
We were considering 4x 5870s vs 2x 5970s, not 4x 5970s.
nster suggested you could power 2x 5970s on a $150 PSU.
When I'm talking about 4x 5870s, I'm looking at the Cooler Master RSC00-80GAD3-US, which is about $240.