I used this gear calculator. John Maher Racing » GEAR RATIO CALCULATOR
After plugging in both your tire sizes you'll see how small each tire change is from stock. Tenths of a mph using the 6100 rev limit.
The stock shift points are good from a torque standpoint. It lands my car within single digits of the torque peak and with the 6400 gear change I land at the peak. The big difference is in the hp at each gear change. I retrieved my hp and torque numbers at each data point from a video of my last dyno. The information on the dyno screen lags a bit but it's as close as I could get. With the 6100 shift and either gear ratio the revs fall to 3719, 3927, 4326 and 5063. With the 3.27 they fall to 3905, 4117, 4539 and 5314. Those 2xx rpms on my car are 15 hp. more from post shift to redline average. If my schooling had made math this much fun and useful, I'd have been much more studious.

Les