If they are close enough the only way you can tell the difference is on your end of the gun.
I shot some 2 3/4 Winchester supreme eliteextended range the other day and it performed very well. 1 1/2 ounces of shot with much less recoil than aregular 2oz.3 inch turkey load.
However, it should be mentioned that as the "target" moves downrange there is a noticable difference in performance (3" vs 2 3/4") in most guns. Not at all unexpected when you consider the differences in the payload of the shell.