Thank you for the detailed reply.
That really changes my approach on this. Granted the current setup works pretty well, I want to future-proof my build as much as possible.
Is there any way to guesstimate what kind of performance increase I will see if I go to the 580 card? 5%? 50%? 100%?
Is there any indication that Sony is going to provide updates to Vegas to utilize the 6XX series cards? It is a little concerning to think about the fact that the GTX670 FTW+ has 1344 Cuda cores (of which Vegas is only using 336) whereas the GTX580 has 512, but what happens in the future? Will Sony add support to the 6XX series cards, and then I lose out on the 1344 Cuda cores in the long run, for essentially the same price?