That's interesting. I did a similar experiment which included various sized moving boxes and moving circles and goal balls from the level designer plus various sizes of sticks and water rods and all three of the wheels.
Everything except the sticks fell at pretty close to the same speed. (Big circles and boxes from level design fall a -little- faster, but it's barely noticable even when dropping from the top of a fully zoomed-out level.)
All sticks and rods fall slower than those other items, but all the sticks and rods fall at the same speed as each other regardless of length. It looks like rods and sticks just need a tweak to some gravity constant.