I just purchased a Gigabyte K8NXP-SLI and 2x eVGA-6600GT Pro cards (they won't be here until monday or tuesday).They should run well because the Pro cards have 1.6ns ram rated @ 550. I'm sure I will see quite an improvement from my the AIW 9700 PRO I use currently.
I eventually want to get 2x 6800 GT (can't find 'em anywhere right now), but due to availability I went with the 6600s. The great thing about eVGA is they offer a step up program. If I apply for the step up (within 90 days), they will credit me the total price I payed for the 6600s. So I pay the difference and send them my cards and they send me 2 6800s.
The great thing about SLI is the options for the future. If the dual 6600s run as well as I hope, I may just use them for the next 6 months or a year and get 1 OR 2 of the great next-gen cards whenever they come out.
I really don't think games are going to even come close to saturating all of the potential of SLI (or even single next-gen cards) for at least 1-2 years. Any game that would be that strenuous would not be playable "by the masses". We just had a big step up in games with the release of Doom 3 and HL 2. These have been in development for years. IMO the next jump won't be for a few more years.
Skeetman