I have thousands of miles on my Ultegra road pedals but not a ton on my SPD mtn bike pedals. Could i swap them? I have the plastic tool on order so i haven't tried opening them to see if they are the same length.

while i'm here.. how fast should the pedals spin when not clipped in.. like on the road pedals i flick them and they fly around. the mtn bike ones seem to have a much thicker grease slowing the spin. not sure which is better