Big Suggestion: Make it so you can choose whether you want no key to be the slow medium or fast speed.
Essentially you would have 3 different modes with 3 different speed options:
1 (As is right now):
None - Slow
Ctrl - Med
Shift - Fast
2:
None - Med
Ctrl - Slow
Shift - Fast
3 (my preference):
None - Fast
Ctrl - Slow
Shift - Med
You don't even have to add much, just a key bind for slow speeds set to None by default.