Thanks! I did a 30 minute ride today at lunch and had no problems this time, but of course that's probably too short to tell. One change I tried to make consciously based on something I read here was that, on the first ride, the weight on my hands when on the hoods was basically pressing down on the webbing between thumb and index finger, which I see is the all-caps warning on your link. Today I tried to focus on letting the heel/side of the hand on the pinky side take the load.

Looking at the pics, one thing I can see a larger bike helping is my knee position -- my knee is a good inch or two behind the pedal spindle, and I can't slide the saddle forward because then I'll be even further forward over the head tube.

I've been meaning to ask, when people talk about rotating the hips forward, how is that functionally different from arching the lower back, or is it?

And holy moly, road gearing is going to take getting used to. I bottomed out the gears on a hill and just had nowhere else to go! Don't know how you guys go up 10+% grades for miles on end. I guess when I end up on the Diverge with its lower gearing, it'll feel like a vacation by then.