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Using the close ratio tranny, a 40T spur, a 10T pinion will give you the same speed given the same motor, voltage, etc.
For speeds in the 35mph range, I would go with the wide ratio tranny option, a 40T spur, and a 14T pinion. That seems to work best for me, and the wide ratio seems to let you use a more common set of gears while still offering some adjustment options.
BTW: I used
this calculator to get this data...