I think:
6.5 = 10 turn
7.5 = 12 turn
13.5 = 27 turn
I agree with everything that's already been said about the 13.5. I would just add that it obviously has less fade than brushed stockers, which makes clearing the doubles at the end of a stock truck race a little bit easier.
IMO, BL LRP is the way to go for 1/10. I've had 3 speedos and 7 motors and they all have worked flawlessly. The Vector series motors w/optional sintered rotor feel like well tuned brushed motors.