Re: GTS450s at newegg, go get'em!
Is a 450 even powerful enough to use for 3D and Physx (while being the main renderer)........ These features you list are mainly enthusiast grade options that are likely going to be run with more powerful cards.
I know the 450 was more a replacement for the 250 and not exactly after the 5770's spot, but considering how long the 5770 has been out, it would have been nice to see slightly better performance. It's still a really nice card and one that could definitely be suggested over the 5770 due to superior multi-GPU support. It might come out looking a lot better in an SLI review (any out there?).