I will say this, waiting for the 'Next Big Thing' is a waste of time in my experience. I'm upgrading my rig soon as well, but I'll probs go for the Core 2 Duo 6600's if that's all that is available and affordable.
The thing is, and I've done it myself, you put off buying things because the 'Next Gen' is only a few months away, then, in a few months, the 'Next Gen' comes out, and not only does it have its own problems that need solving, but there's already another generation of tech on the Horizon.
I tend to find it's best just to get whats available at the time, or you'll be hanging on better stuff for the rest of your life