I took out 4.10's and installed the 4.30's in my car (right before it dropped a valve) and immediately noticed a difference in the ole "azz dyno"!!! Well worth it!
I drive a stick, with an .68 Overdrive, so the freeway thing really didn't affect me switching to the 4.30's. An auto may react different, but I doubt it. I've found over the years that you can handle more gear than you think you can. I say go for it. In short:
DON'T FEAR THE GEAR!
