Why are you getting ahead of yourselves? How can you determine the gear, with out knowing the MPH you will be turning, and the usable RPM of the engine combo, and car weight?
I have run anywhere from a 3.91 with a 26 inch tire to a 4.56 with a 22 1/2 inch tall tire. It all depends on the combo. Differnt car weights, different rpm range, 1/4 or 1/8 mile.