well you have to know that the taller tires throw your gears off also.
But to be blunt, throw 4.56 out the window. You'll go 45 and pull 3+ grand on the tach. Plus with a stock motor, you'll fall on your face around 60-70.
4.10's isn't bad, allen likes his, really nice off the line, my only problem with that is i think he is running 70 mph and pushing 2500 or so.
If you keep the 3.73's and with the 20's, i'm going to guestimate, you'll have around a 4.10 gear ratio, i'm not how to config it, but i'll ask and get a def answer tomorrow.
btw, what 20's are you going to run? what size tires? do you plan to bag in the future?
91 s10 - bagged and bodydropped...getting rebuilt
91 nissan - backhalfed and bagged