Bottom bracket height is a tad taller on the BFD than the Big Dummy, which makes sense, considering its intention. Standover height is similar between the two, with the Big Dummy being an XL and the BFD a large. With the exception of the fat tires, and the Big Dummy being set up with a Rohloff, I have them set up similarly, and sometimes can't tell a difference between the two, fit wise. The BFD is set up to take an internal dropper seatpost, which given its taller bottom bracket height, is something I'm considering doing.
The bags and platform/deck sit higher on the BFD by 3 inches or so, and sit further forward in relation to the rear axle by 1.5 inches. So, you lose some stability with a higher center of gravity, but get it back with it being further forward between the wheels. I've had over 30 pounds of trail tools on the deck on single track, and didn't have a problem.
I'm car free, so the BFD sees about 50/50 road and dirt. If I know I'm going to be doing a lot of pavement pounding with it, I'll throw some extra air in the tires, or adjust as I go, as I keep a pump with me. I've found 12-15 PSI front and rear is a reasonable compromise for good dirt traction and reasonable rolling resistance. With the tires up around 18 PSI, it rolls pretty quick and handles sharp, though you lose some traction, float, and suspension compared to lower pressures, just like any fatbike. I will say, it handles dirt better than the Big Dummy, even with the tires pumped up hard, and it does even better with some weight on the back wheel! I've actually gotten so used to riding the BFD on dirt, I have a hard time going back to a "normal" mountain bike.
Yeah, if I had to choose just one, even if I were doing mostly pavement I would have to pick the BFD, as I feel it's a more versatile, stronger frame. (My Big Dummy is an older one, but I've ridden a new style with a load, it doesn't feel much different.) But I've got some sentimental attachment to the Big Dummy, and won't let it go, and it makes a great roadie cargo bike.
