I guess I might be uniquely qualified to answer your question as I have both a Hampsten SB ti and a Calfee Adventure Tetra Pro. I spend a few months of the winter in the Texas Hill country and rode them both for a total of about 3500 miles. FWIW, I also have a 700C Tetra Pro.
My Adventure has 650b wheels and disc brakes with TRP Hy/Rd's. I'm running a Shimano 10 speed group on it with a Sugino 901D crankset and BB. I'm using Compass Babyshoe Pass 42mm tires mounted on Velocity A23 rims.
Here's a picture:
OK, with that lengthy intro out of the way, now to answer your other questions. Firstly, I've never ridden it on the trail nor even on gravel that much so I can't really comment on that although my guess is that it'd be great. What I can say is that on Texas chip seal the ride is about as good as it gets. Those 42mm 650b tires do an excellent job of smoothing out the ride and roll pretty well. The overall ride? Well, it's a Calfee which to anyone who's ever ridden one is about as positive a statement as can be made about the bike: excellent, predictable handling, smooth ride, great all day comfort and responsive when you stomp on the pedals. No, it's not a crit bike nor would I say it's anywhere near a bike you'd go racing on but if your plan is long rides on sketchy pavement I don't think you can go wrong.
I conducted a number of "calibrated idiot" tests where I supplied the idiot in which I rode the Calfee and the Hampsten on the same route under very similar conditions. The route was just under 50 miles and I rode as hard as I could for that distance on both bikes.
On average I'd say the Hampsten was about .5 MPH faster than the Adventure and I put most if not all of this down to the larger tires (I had 27mm Vittoria Paves on the Hampsten). I think for even moderately decent roads that 38mm tires are the sweet spot for 650b's - big enough to provide pneumatic shock absorption but lower rolling resistance.
And just for the heck of it, here's a shot of my Hampsten. Note that in the picture it's sporting 32mm Compass Gran Bois 700C tires.
I've done 200K brevets on the Calfee and brevets of all lengths up to 1500K on the Hampsten. The only reason I've chosen the Hampsten for brevet work is I've outfitted it with the necessary add-ons such as a dynamo hub, bags, etc., needed to do long distance self supported rides. Having said that, a friend of mine did the TCR on a Calfee Adventure so I think it just might be up to the task as well
Fire away with any questions and I'll do my best to answer.