First test in the books, no major issues other than my half-assed rubber grommet solution for the shift cable slowly failing. I need to figure out what part actually goes there soon, for now I put a random plastic washer over it to keep it in place-ish.
The bike is definitely faster for the same effort and more fun in general. I still only did 17 mph at 170 bpm but that beats 16 on the same route last week for a similar effort... braking, accelerating, climbing, descending (such as it exists here) are all quite a bit easier/better. Crosswinds are a lot more noticeable but will hopefully be not bad enough to be dangerous.
Ultegra R8020 shifting is absolutely no better than Claris R2000. If anything it might even be slightly worse to be honest. The only reason to get this groupset is to have hydraulic disc brakes with levers that have adjustments for both reach and free stroke - which is valuable to me but somewhat annoying that it costs so much to get those features.
I think that the only part I'd do differently so far is to get a smaller/lighter cassette and perhaps the short cage derailleur to go with it. 11-36 seems like way more than I need on a fast bike. The biggest gear I used today was 25.
I'll ride it as-is for awhile before making that kind of change.
Also 25mm GP5000TL on a stiff carbon bike is really no different in comfort than 25 or 32mm on the floppy aluminum one, assuming pressures are adjusted about right. Bumps still suck but not unbearably so. I might cancel my backordered 28mm's and stick to 25 at this point for the weight/aero benefits.
on a moderate budget. Fancier 
and cassette could drop another pound, otherwise there's not a hell of a lot of room to get lighter without spending big $$ on dura-ace shit.