A couple of things: Vertical dropouts shouldn' affect the stiffness of the rear triangle, however they make it easier to remve the rear wheel on a touring bike with wide tires.


Chainstays can be long and stiff or long and whippy, a lot depends on the tubing. I think a bike with long chainstays might be more comfortable on a long tour.


Some bikes are designed to carry weight on the rear; many British bikes were. Others were, and are, designed for a front load, in the French style, perfected by some American and Japanese builders. I think a properly designed bike handles great if not perfectly with a front load, but that's me. A lot depends on the head tube angle, the fork offset and the resulting geometric trail. Tire width also affects the handling. And then there is wheel flop, which I don't completely understand.