I'm getting ~540 Mhash/s now with 2x 6950's OC'd. That sound right?

Also, does it make more sense to join a pool or just mine solo? What's the recommended pool if I should join one?

I'm looking at http://mining.bitcoin.cz/ vs http://btcmine.com/ vs http://deepbit.net/

With my type of system, what's better? Pay Per Share, or Proportional? I don't really get it...

Oh yeah, and I still have the question if I should be running my miner with flags specific to my GPU's? I saw stuff like -128 f1 or something like that? What does that do?