You really don't. The Core 2 Duo systems beat anything AMD has to offer right now in overall performance, and do so quite handily.
As for the new platform, I don't consider Santa Rosa worth waiting for if the Merom-based MBPs launch soon.
The FSB will give you a small speed boost, the IO is slightly improved, Robson (flashmem cache) will probably make the biggest difference to most people, esp if your apps hit VM a lot.
Overall, tho', it's all incremental... and you can wait forever...
I mean, Penryn will debut the SSE4 instructions and that's probably only a year away... <G>