I'm getting pretty much the exact same MPG with my 3.4 that I did with my 20R. But I get where I'm going a hell of a lot faster than I used to. 
A 3RZ is a great mix of power and fuel economy if you're concerned with that.
I have thought about going that direction, I havn't really decided where to go where with it. Plus I don't really have the wallet to go too far with it
