After putting some more rides in, some longer ones, and in some strong sustained winds (20mph sustained), some more feedback:
* the bike feels magically alive! Like some of the best old steel bikes there is a delightful vibration in the bars and through the seat that feels even better when you're leaning into the bike and making tracks. Great feel. I have missed this "live wire" vibration for some time.
* bad pavement, chip-seal, and general roughness are muted to a great degree (running 25mm tubulars on zipp 404s with ~85psi, and specialized Romin Saddle - I weigh 82kg-ish).By comparison my '08 Cervelo R3SL with the same wheels brought out the bad pavement feel much more unpleasantly.
* Test rides on a specialized venge felt slightly rougher, slightly faster handling, but no magic in the frame feel.
* test ride on a s5 - much less muted ride, weird riding-a-board feel, floppy front end. .. no room for 25mm tires - yikes.
* big bumps require one to get out of the saddle - the bike is not forgiving over really sharp impacts or large bumps, slightly more unforgiving than my other race bikes (Look, cervelo r3sl, cervelo r3, cervelo r5 ) I have ridden lots. This is weird because the small stuff is very muted, but the big stuff hurts. The cervelo "r" bikes seemed to float over large impacts, but bother ore than the bmc tmr01 with rough roads, this one is the opposite.
* the "muted" feel - or "planted" feel - makes it feel really confident over rough road, so that you feel that power is getting to the ground.
* the handling is neutral to slow, very relaxed and stable compared to say a r3sl, which was my daily driver for a long while. The bike is very balanced, and no problem riding in a pack etc, but doesn't require much attention to keep going. By comparison the Giant propel was twitchy, and my cervelo r bikes also felt twitchy. This kind of reminds me of the great neutral-to-slow handling my 90's-era Trek (5900 OCLV carbon) frame had.
* it is a BLAST to put down sustained power on this bike, and easy to get into rhythm, as the natural vibrations of the frame are compelling, and you can feel and hear the speed pick up. On a recent ride a guy jumped on my wheel and said my bike "sounds cool - what is that?"
* People keep saying its stiff, but most good frames are stiff enough these days, and under serious power most wheels and bars flex so much that I can never tell when I am really going nuts in a sprint what is flexing. (OK - I am heavier than most at 82kg and pedal harder ~1500w during sprints than most to make up for that, so I haven't yet ridden a bike/wheelset that doesn't flex enough under power to rub the brakes). After almost 30 years riding, I know this frame feels stiffer than my old 80s-era steel frames, but is stiff in different directions than my r3sl. For instance my r3sl used to jump in the air and sideways sometimes during hard sprints full-out (during the initial acceleration). I know this is my bad form, but the bmc doesn't do this. When honking up a steep hill, the r3 also used to slip the rear tire if I wasn't careful to lean back, but the BMC also doesn't slip. Perhaps this is the weighting, but I also think that longer stays and a smaller rear triangle without a brake bridge may help the bike flex vertically - that is just guesswork, but it does feel good.
* High speed (up to 60mph) and low speed alike feel great - bike was always stable and handling relaxed.
* no problem riding no-hands even in blustery conditions. The bike has a very good centering feel, and easy to control rate of lean.
* cross-winds of 20mph saw me leaning less than other bikes I've owned, and never felt that the bike with 404s was hard to handle, or had that weird front-wheel-as-a-kite I've sometimes felt when the front end seems to pick up more wind.
* your guess is as good as mine. My impression is that there are so many other factors that I am OK being wrong, but because I've ridden so long with a power meter on the same roads with the same clothing, gruppo, wheels, etc that I think I am seeing a consistent 10-20w drop at the same speeds over my previous daily driver, the r3sl.
* I did choose zipp vuka sprint bars, went nuts on my cable routing, used a garmin integra stem, and also have a behind the saddle bottle mount now, so I am guessing that the 20w is not a fluke.
* the front brake rubs my wheel when I sprint, even if I have zero cable tension, because they don't open wide enough. I may have to completely remove the washers and see what I get, but I think the brake pad holder is the issue. . .maybe time to take out a dremel.
* I put rotor power cranks with a 30mm spindle into this 41mm BB using the enduro BB - 4130. Rotor sells the same BB. It has a lot of drag I believe because even with no washers the cranks place some lateral preload (bad ;-( ).
* cable routing was a real bear. Took way too long, but their video was very helpful.
* I used zipp vuka sprint bars with internal cable routing This made the routing work worse.
* I also used the garmin integra stem - not sure I would do it again - since the steepest stem they make is a -10, the garmin mount goes up at an angle! Why bother making that stem and omit the -17 110 size? Why? -17 would have been amazing with this ~73 head angle.
*brakes are really sensitive to cable housing length, which can cause the noodle-side arm to move little and the other to move a lot. I understand getting a flexy noodle solves much of this, but I have too little interest in that to open the thing up again.
* brake feel is great - better than my sram red brakes in power and modulation, as well as lever feel. Totally usable to me.
* Tour magazine says this frame loses 3-4 watts with frame mounted bottles/cages, so I went a little tri (I am embarrassed to admit, as a life long roadie) and used behind the saddle bottles. I used x-labs, but I really want torhans to make a aero-20 like http://www.torhans.com/index.html#Anchor-AERO-49575
road-bike handlebar aero drink setup!!!
* Looks are wonderful - this is the best looking bike I've seen in a long while, esp when built up right
* happy I chose this frame - magic vibration in this frame
* handling is neutral which means I can ride longer more relaxed, trustworthy steed with no bad manners.
* inspiring looks, especially when coated with road grime!