MrWicked has lots of experience with these and his recommendation of 150 lbs torque would likely be the top end, maybe he will confirm. It may even be required on modded carts.
The factory specs call for the torque on the castle nut to be 90 lbs with a maximum of 140 lbs. When installing the cotter pin, do not back off the castle nut, take it to the next notch.
This is for a stock golf course cart.