with all other factors the same (speed, angles, acceleration, transmitted power etc) then - with portals - the shaft will be turning twice as fast and hence carrying half the torque. So half the turnover effect.
My tuppence worth.
TS
Incidentally - for the same reason my father was taught (in WWII) not to use the transmission brake on a jeep while the vehicle is moving in case it flips it over. Anyone know if there is any truth in this one?