I thought I'd chime in with my findings before going to bed.
I got my USB-C to Lightning cable delivered to me today, and I spent some time draining my iPad Pro battery with multiple runs of
GFX Bench Metal's battery test. I drained it down to 10% then started to get it charging. Here's a screenshot with
@echo1877's excellent app (sadly no longer on the App Store):
As you can see it indicates 2A / 29W charging (I guess the app needs to update the "max Power" for the iPad Pro)
I turned the screen off and left it charging while I went to do some stuff. I came back about 2.5 hours later and it's
fully charged:
I'm personally very impressed by the charging speed. I've ordered a second 29W power brick just for this - decided to save a little and get a
used one from Amazon for about $30.