I would have to say it depends on your gearing.
With my car by the time it's going into lockup I'm doing already doing 75-80 and I'm lifting off the throttle to get my cruise speed.
My motor is about 350-400 and I don't have any problems with it, and we have to remember these were truck transmissions rated for towing 6,000 pounds on top of the trucks being 1,000 lbs heavier.
I turn OD and lockup both off if I'm getting into it that hard and then switch them back to "auto" mode when I'm done.
I take it the hollow lockup shaft is your concern?
