Glad you're enjoying the new bike, though I share some of your opinions, other's have me scratching my head:
I now know what an EBB is. I changed the tires, the chain went back on loose.
This one has me completely puzzled. you changed the tyres and the chain went slack? I can't see how that happened!
As for the bad run of punctures, just how much heavier is the new bike! It's hard to see how an extra couple of kg's are responsible, maybe if you were already on the limit of race tyres, but those Armadillos look pretty tough (I haven't used them) Of course if you load it up with twice the maximum recommended, it's also a good idea to increase the pressure to match, but you probably knew that.
I notice from your first post that you stopped recording on Strava, maybe it's time to do so again. The impressions of speed, drag, momentum, don't always match the reality. I've had a few excellent Audax/Sportive bikes that
felt so much quicker, but the numbers showed the difference was nothing like as great as the impression. The hub does sometimes feel draggy, but these things are measurable and the difference is minimal. Likewise uphill, yes I've had bikes that seem to fly up the hills in comparison, but again, for me, the reality is there's little difference. It's possible that as the speed increases the gap widens, I wouldn't know, but it's the numbers that will show that rather than the impressions. The claimed independent Rohloff testing showed the efficiency increased at higher input, indeed they were criticised for using these figures, rather than the more average riders input.
You're out of luck looking for a lightweight steel disc fork, there's no 853 option, seeing how easily 853 crumples in an accident I'm not surprised. The weight difference between your fork and an 853, is less than the difference between your change of front tyre.
I've described the Mercury elsewhere as a midpoint between an Audax and touring bike, I Audax on mine, but then I tour my way around Audax. It's a shame IMO the attitude it's a race has become so prevalent, there's always been a wide range of riders, but that has become narrower as the popularity increases. Fine for those riders of course, they can ride however they like within the reg's, but it has changed the sport with more organisers catering for that group to the detriment of the 'tourers'. A decade ago, steel touring bikes made up a huge proportion of the average field, now they're very much the minority, I blame the relaxing of the mudguard rule! It's made me a lot more selective in ride choice, though there's still more on the calendar than I'll ever get to do. maybe I'll see you on one, though it'll probably only be at the start!
EDIT - And where's the photos? Are you riding so far and fast that you don't have time for a pic or two?