Stiffness to me feels harder over bumps. Not as smooth of a ride. There is stiffness and stability, which can be related but are different. Confused??? I rode a Giant TCR (don't remember which model) and it felt really stable, but way too stiff for me. Stability is hard to describe, but the LBS guy thought it was a good term. The front end of the bike seemed less wiggly. That's probably not a good term. How about less motion/less fluid/less flexible. See - hard to describe. It was not a bad thing. I ended up with the Pilot because it felt right. It was a smooth and comfortable ride and the geometry worked for me. When I took my bike into the LBS after the crash, the owner did the testride after the repair. He even commented on what a smooth ride it was.

I can't really comment on the upright position. I don't feel terribly upright. My seat sits just above the handlebars. I came from riding a hybrid, so anything with a lower body position from that felt aerodynamic to me.