Just to add this to the conversation . . .
Last night I went on another ride. (Unable to ride since Sunday morning due to work and high water from heavy rain.)
Last night's ride was on much smoother pavement and my hands didn't go numb until much, much later.
Sunday morning's ride had a lot of wavy concrete on the road which vibrated the fork so much that if I pulled one hand off the bars the front would shake so much that the fender would vibrate into the tire. That's the ride that made my hands go numb in about 10 minutes. Arrrgh.
Anyway, I got notification the 25 degree stem (original 10 degree) I had ordered had arrived at my work. I'll pick it up this weekend on my way out of town for work.