In about a month I plan to build myself a new Ivy Bridge based PC, in Antec Solo2 (or I may reuse an old P150).
I'd like to know which currently available fans move more air than the included TrueQuiet, at a rpm of about 600.
My current PC uses 800 rpm Slipstreams in a Solo, manually controlled and fixed to ~600 rpm, cooling an i7-920 and Radeon 6850.
The new PC will have i7-3770 and either GTX 680 (in a Solo2, probably doesn't fit in Solo) or Radeon 7870 (in old P150).
So should I keep the TrueQuiet, replace with Slipstream, or use something else, like Cougar Vortex or Bequiet Silentwings?
If I go with 7870 and old P150, the question becomes: which fans are better than a Slipstream?
If I can get a fan that's significantly better than a Slipstream and a GTX 680 with a beefy VRM setup, that can be cooled quietly,
then I'll go for the Solo2, if I can't then I'll go with old P150 and 7870. Thank you in advance for your answers.

The 800 rpm slipstream is a good fan. If you like it why change?

I'd give the SlipStream a shot before I consider replacing it.