advise on an upgrade

[Monkey]

Hi ive been running a maxx with a 9920 controller and 9L motor for nearly a year now and have read about the XL motors giving more torque and running cooler so would like to upgrade but which turn should i got for im running 16 cells IB3800's and would be happy with about 20min run time so whick of the XL motors would be better for me? Also there is no option for the shaft size on these so are they the 5mm ones or standard?