I've got numbness in the left hand after similar ride lengths. I use a nearly flat bard (~5 Deg) and Ergon grips. I am left-handed and also in IT...so lots of mouse use from the left hand during work day. Numbness seems to be in a few fingers, never all or whole hand. Appears 20-30 min in to the ride from work. Dissapates if I lift thumb from under the bar to the top....but that doesn't feel secure over bumps etc.

Had a professional bike fit session and they tried raising the handle bars to their max and lowered the seat 1/2 inch. Seemed to help a bit, but not completely. before I could make more changes to setup the bike was stolen so I'm starting over with a new ride...getting another fit this weekend.

Interestingly, I hear opposite advice from bike techs vs physio therapists that do fits. The bike guys seem to focus on seating position as the main issue while physio guys spend lots of time on the bar adjustments.