Did you go to this part of the Shimano site?
http://techdocs.shimano.com/techdocs/index.jsp

Cursor over the road or mountain group and you can see a list in descending order.
It doesn't really tell where road compares to mountain though.

I certainly wouldn't claim expertise in bicycle geometry and I'm sure you have to consider various factors beside wheel base etc. (the whole package)
However, think of a longer wheel base bike being like a bigger car. It'll ride a bit smoother, but handle a bit more sluggish. (or less "twitchy" if you prefer it that way)