FYI... Shotgun shell lengths are named for their length after firing (i.e. chamber length). Most often they are about .5" shorter in length before firing than described on the box (e.g. 2.75" shells are about 2.25" in length).
Your goal is to size your magazine and extension/limiter to hold about 5.75 x <Size of Chamber> shells. If you have a 3" chamber, you should be able to hold 6 x 2.75" shells (but not 6 x 3"). If you have a 3.5" chamber, you should be able to hold 7 x 2.75" shells (but not 6 x 3.5").
That way you are never exceeding the 5 x <Size of Chamber> magazine limit for semi's, because the 6th chamber-size shell won't fit in the magazine. Make sense?
Bottom line, if you want to max things out, you'll need an extension. Whichever way you go (tricked out VersaMax or NC extensions), Casey at TacOrd is great to deal with.