Well no doubt from what little we know of NV30 it should be faster, but I doubt it will be hugely faster (leap frog seems certain over the next 12 months). However, we really do need to rem Parhelia and how double the RAM bandwidth of a GF4TI4600 didn't translate in to anything significantly better than GF3 3D perf. It will be interesting to see, but as said Rad9700 is awesome and out now.
I personally can't afford much more than 100 notes on a gfx card but at least that tends to get great perf to cost and devalues very well too. I'd suggest waiting if only to get the DX9 hw (and gen 3D perf) for a cheaper price, it won't be too long before $200 versions of Rad9700 and NV30 are with us and for me they are worth waiting for considering GF3 and Rad8500 are more than capable of running all current games well, but then if you have the cash cool!