I am late to the party.
My understanding is that at anything above walking speed bikes steer by camber thrust, not slip angle, and the bars are turned (steered) to keep from falling over.
As was pointed out in one of the early posts, rake and trail (and to a lesser extent wheelbase) really affect the handling at speed. That is why it is easy to ride no hands on a touring bike or cruiser, harder on a crit bike.
Having said that, stem length will affect weight distribution, although probably not any more than going between the tops and the hoods.