[Max Lobovsky]

There is probably room in the gearbox to shift ratios so that the shifting gears are spinning faster with less torque. Specifically, increase the size of the CIM pinion, then increase the final stage ratio.

I assume this is all 20 pitch? As I'm sure you know, make sure to buy the strongest material that you can find the shifting gears in.

A good question that I can't answer is wether extra backlash is a good idea for the shifting gears. More backlash means they will be able to shift faster (less friction, more time to do so), but more backlash also means they are slightly weaker. I'd guess a few thousandths extra is a good idea, but this is definitley a question to ask someone who has built a sliding gear shifting gear box.

Also, where are you purchasing that long gear in the final stage?