Not really directly addressing your questions, but FWIW, I'm just sitting here, reading, so ...
I'm 5'9", with a 29" or 30" inseam (I buy jeans typically at 38W30), so I'm not tall. Unlike your upsizing, I downsized, from a 650 Burgman (actually, I had two of them, over the years) to the C 400 GT this past June. I find the 400 a little more cramped, in terms of leg room, than the Burgman: I can't completely stretch out, but I've gotten used to it, it doesn't bother me, etc. And my knees are still lower than my hips, so all in all it's just a minor change for me, i.e., bending my knees a little more than I typically had them on the Suzuki.
In terms of the suspension, yep, IMO it's what bike-magazine writers often pen: "built to a price point." But, then again, so were the suspensions of all the bikes -- from baggers to scoots -- that I've owned. I think this is pretty much the case with all bikes, unless you're dealing with the absolute-top-spec sport bikes, the ones with Ohlins suspension built in, that sort of thing. I changed the shock springs on my 2000 Valkyrie, for instance, and may change out the entire shocks on the 400. Or may not -- I haven't really decided. In case you haven't read this thread yet:
I upgraded my rear suspension with YSS shocks. I considered the Ohlins but decided not to because of the price…..$1,100 USD vs $510USD for the YSS. I only ordered the rear shocks and not the front cartridges. Wasn’t sure if the costs justifies the costs….cost of the YSS cartridges and...
www.bmw-scooters.com
The two things that annoy me about my C 400 GT -- and I try not to dwell on them, just "get over it" as a friend is fond of saying to me -- are:
1) The lack of cruise control. Given that the '22 has ride-by-wire throttling, umpteen sensors, a nice TFT display, etc., it seems to me like it would be trivial to add that.
2) The Schrader valves in the "spokes." This may make checking air easier -- I've added sideways valves to many rims over the years -- but it precludes adding a TPMS sensor to the front wheel (because it would hit a brake caliper). I did add a new FOBO sensor to the back wheel, so I'm halfway there. If BMW is going to go against the grain, i.e., not put Schrader valves in the rim like every other manufacturer, the least they could do is offer a factory TPMS for the 400 (which they don't).
OTOH, the C 400 GT is my favorite bike over the last 25 years.
It just invites me to hop on and go for a ride. This may also have something to do with its being the lightest bike I've owned, coupled with my not getting any younger, but it also handles superbly, accelerates and rides very smoothly, brakes well, and looks sharp. I put more miles on the 400 this summer than I have on any bike in quite some time.