In the types of guns we are generally speaking of here, upper crust British guns, those with 2" chambers vs those with 2 3/4 chambers will not usually be "Otherwise Identical". The 2" guns will be lightweight Game Guns, while the 2 3/4" ones will be heavier wt pigeon, trap or wildfowl guns. Which of these a man would pay the premium for would depend more on the type he was seeking, not on the actual chamber length. If he were seeking a light fast handling grouse gun for instance he would not pay a premium for a heavy gun in order to get the 2 3/4" chambers. He might just pay a premium to get a slick little 2" chambered gun.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra