I think Cbabes hit it on the head here.
It all comes down to your reloading method, and whether your system can accomodate the shorter shells.
Squeezing 10 in the gun is fun, but, you have to be able to feed it from the belt if the stage is bigger than 10. That's where your loading methodology comes into play, and it needs to support the 2.5" shells as well.
That being said, you *could* run different shells based on your start, and reloads.
So, you could go with a hybrid solution.
Of course, that can lead to ammo mixups, and wasting time, or fumbling a reload, or whatever.
I think the KISS principle applies, and, it's your reloads that will make or break you, as, you don't always start with a full gun anyways, and you don't want to be messing with different ammo lengths from stage to stage just to find that edge. Smooth and steady, and consistency is key.