Whether any individual would pay a small bore premium really isn't the question. Rather, it's what the market shows. I think somewhere in the 25-33% range is accurate for Brit guns. Might be even higher for American "classics". You can find a decent Sterlingworth 12 for around $1K. Good luck finding a 16 in the same condition for much under $1500. I think one reason American 16's hold their edge over American 12's has to do with people looking for something in the "game gun" weight range for upland hunting. There are plenty of Brit 12 game guns out there, weighing pretty much what American 16's weigh--and a lot less than your average American 12. So the same individual who might opt for a Brit 12 and pass on the premium for a Brit 16 would likely stay away from most American 12's.
