Originally Posted by DannoXYZ

You could get a smaller large-chainring and that'll let you use a shorter BB-spindle. Most bikes are geared for 45mph+ top-speed of pros, most people end up hardly ever using their big-chainring as a result.

Also, the chain coming down when spinning backwards is due to the angle of the chain. It's aimed over towards the outside at the top after it comes off the big bog. It's like there's an invisible derailleur on top pushing the chain sideways. Just be sure to be in the small-chainring when you're using the three biggest cogs in the back and it'll reduce this amount of sideways chain-flex. Less-friction, the chain will last longer and you'll go faster as well.