What about relative top tube lengths and MTB geometry? I assume that touring bikes would have a shorter top tube so you can sit more upright, while racing bikes would be longer to facilitate an aerodynamic position--but I'm just guessing.

Let's assume a MTB is the fully evolved sloping top tube type.

For example, I've always wondered if the effective top tube length of a MTB was also relatively longer to facilitate you're getting lower and thus having a lower CoG, but again I have no idea.

These questions have always puzzled me.

Also, trail: I assume that the frame angles in themselves don't make a huge difference to handling, though maybe a shorter wheelbase (which can be achieved with steeper angles) might make a bike more nimble.

I assume that a touring bike would have more trail for stability at speed, road racing bikes maybe a bit less, while track bikes, cyclocross, and MTB would have short trail for nimble handling. Is this about right?