hey secret weapon
7.91 is a high gear ratio (using a 70 tooth spur and 23tooth pinion) but u might not get enough top end out of that
6.27 is a lower one(using 70 tooth spur and 29 tooth pinion) and that might get you the top end you want...
somewhere in the middle there
mainly depends on how large you track is and also how big your tires are