Did you do the math???
4.88 divided by 3.91 equals 1.25... a 25-percent increase in finish-line rpms at the same speed.
If you're taching 5,000, like you say, with a 3.91, that will put you through at (1.25 X 5,000) 6,250 rpm.
If that's what you want, great; I don't know at what rpm your engine "peaks."
You'd generally want it to run through the finish like traps at about 10-percent (rpm) OVER your horsepower peak.
A 4.56 would put you through at (4.56 divided by 3.91 X 5,000) 5,800 rpm.
Just food for thought....:burnout:
P.S. does your transmission have the 2.74:1 first gearset? If not, I think that would help your launch somewhat...