OK, I love this bicycle. I am admittedly still riding it ridiculously, in upright position half the time and slowly and easily when I am in aero. But it is a beautiful piece of machinery - I can feel how good the components are! - and it is more similar to my road bike than I would have imagined. I didn't ride as long as originally projected, but only on the sensible grounds that when trying something new and a bit daunting, it is a good idea to stop while it still feels genuinely easy and fun and enjoyable.
Will do my long ride tomorrow on the road bike, then ride Thursday on this one again, doing some hill repeats on River Road (mostly traffic-free). My road bike has a triple, so this definitely will take a little getting used to for long steep hills. Also saddle v comfortable in aero but hard under sit bones upright. I have another pair of shorts with better padding there. Will wear those Thursday!
21mi, 1:45 (slow from caution rather than timidity, and much easier effort than my standard ride - this bike will be fast one I get used to it!)