Ok, Im going to give you some gear calculations based a five speed transmission, the T-45. Theese gear calculations are also based with a 26in. tall tire w/ 4.10 gears.
I calculate 113 mph w/ 4.10's, 26" effective tire diameter, and 6000 rpm. 4.30's would be 113 x 4.1/4.3 = 108mph.
If your tire diameter is bigger, multiply whichever number (108 for 4.30's or 113 for 4.10's) by your tire diameter divided by 26. If you want a different engine speed, multiply by the new engine speed/6000.
It is: speed = (rpms x diameter x 3.1416 x 60) /(rear ratio x 12 x 5280)
or, more simply, speed = (rpms x dia.) / (336 x ratio)
If you want to check it for other gears, just multiply the trans ratio by the rear ratio, and plug that total ratio into the formula.