I am not good with numbers. But beyond a point, the difference between IEMs is indeed about 10-15%. The devil is in the details - what that 10% contains and how important it is to your preference is all that matters. IMO, as we go higher up the ladder, even an objective 2-3% increment in one area is enough to make one IEM dearer and shun the other. Also, one man's 'bright' is another's 'right'