What sort of box are you running Acadian? C6?
I probably wouldn't be going any lower than 3.9 if your going to be doing much highway driving. Even then you'll be up over 3k rpm at 60-65mph.
My old BB Merc had a 3.5 gear and that seemed to be pretty close to best of both worlds. Good on the highway and round town and not too bad off the mark.
[addsig]