Rick,
For a long time I thought changing my rear gearing was the answer. Then realized after doing some homework that an overdrive tranny is really the way to go. I installed a T5 with .63 OD and that got me to 2500 rpm's @ 80mph with a 4.57 rear. The whole swap cost me between $400-500.
Doing a 4.10 isn't going to get you much. Use an rpm calculator and you'll see what I'm talking about. At 60 mph you'll save around 300 rpm. Even a lousy .86 OD tranny would get you 450 rpm. Make it a .72 OD and now you're turning about 1000 rpm less than a 4.57 rear with 1:1 tranny.
rpm calculator -David
