just coming off of acl/mcl reconstruction of my left knee, and I've been looking for a new bike for my rehab program. (once I'm cleared to get off the spin bike)

I'm 43 and avid off road motorcycle rider. I do have a trek 4300 hard tail that I have been riding on the road for exercise and rehab purposes. I put slick fat tires on it and trekking bars and can do about 30 miles in the very hilly area that I live in.

I've been looking for a full on road bike to make the ride a bit nicer but came across a basically brand new BB 5 for $850. While I know it's not going to be as efficient has a full on road bike, it's in my budget and looks cool to boot.

my question is: Will it be that much better of a road ride than my converted trek? or should I keep looking for a full on road bike?

I should also mention that I live in a very rural area and the roads are not always the smoothest. although I see plenty of roadies around.

also can anyone comment on the BB sizing, I'm 5'11" with a 33" inseam, and this bike is a size L

Thanks,
Andy