the difficult part about that is the "same ole same ole" with tech stuff: when is it time to bite the bullet and decide?
r420 rolls out, nv40's arent to be seen. the 800PRO shows fantastic speed over last gen parts, and leads almost all benches vs nv40. nv comes out with "updated" (i say that as they're still not avail from nv's site, even tho there's certainly some nv40s shipping now) driver, and "previews" of sm3 combined w/ the driver shows nv now competetive with ati, and in some cases, faster in a DX game such as far cry.
ati most likely will come up w/ improved drivers, the nv... do you get one when ati has better #'s, or when nv does? see, for performance, it's simply too close to call.
overall, the more important factors this gen seems to be personal preference, features, what's avail. and for what price.
i don't see sm3 or 3Dc having a huge impact this generation, but all else being comparable, my opinion is to go with nv40 and sm3 (among other features). in all fairness, 3Dc may show some benefits as well, however overall sm3 seems to have more potential to be the more beneficial feature, at least at this point in time.
i'll end up having both nv4x (still kickin on whether to hold out for PCIe, due mainly to an SLI option which may or may not be a feasible. too many unanswered questions at this point such as motherboards, heat, power requirements, and so on...) and r420 this gen, but at this point in time, if i had to choose one over the other, i'd go with nvidia, simply because the more useable features mean more to me than a few fps one way or the other....