RE: transmision gear and spur gear questions
keep in mind that having a 2 speed means the tranny has 2 ratios, and also you can change the tranny ratios for both 1st and second. You can gear down and go close ratio on the tranny gears and you will get a climbing/dragging/pulling monster that won' have all that much top-end. But if you go wide ratio on the tranny you will have a nice low bottom end while maintaining adequate top-end, or even a high low-end and an extremely high top-end, depending on the spur and pinion ratio you go with.
Although, I have to admit I know nothing about the availability of internal tranny gear sets. I do know that you can get both close and wide ratio sets, but I don't know if you can get the individual gears to do your own setups.
I'm still working out the best pinion to spur ratio for myself. Once I nail it down, I'll probably get a wide ratio gear set, for versatility.