Otto:

While the length/cross-section are the same, the difference is from the cockpit door forward.

I wouldn't want to jumpseat in a 737. 757, I could just about take a nap on the floor. Lots of room for roller-bags.

I've never flown either airplane, but jumping, I would say the 757 is quieter for the guys up-front.

By accounts I've read here, the 757 significantly outperforms the stretch Guppy in climb and load-capacity at hot/high airfields (supposedly why UCH is putting the A-320 into South America).

Neither airplane is a joy to load as a passenger, but with the mid-fuselage door on the 757, if you were going forward, the unpleasantries ended sooner. I have ridden in the last row of an -800, and could not WAIT to get off the airplane.