I ordered smaller pinions also. Installed the 12t that came with it and haven't changed a thing. Plenty fast in 2nd speed. Almost too fast if there's such a thing.
I have the axe 550 3300kv on my defender and after last firmware update, its slowest speed is so slow you can't tell it's moving unless you stare for a while. Oh and the torque is crazy even at that low speed. Can send a dropbox link of a vid