Re MPH vs gearing, the difference between 3.55 and 4.10 when my car was in the 12s was negligible. It ran 12.4 at 112.7 with 3.55s and 12.2 at 112.7 with 4.10s. The MPH only changed when the tire & gear combination resulted in the engine over-reving, and then it dropped off by 2 to 3 MPH.