If you look at studies of the muzzle velocity vs. barrel length, you can see that it is non-linear, and so at shorter lengths (10.5-12.5) you get more return on increased velocity for a little bit more barrel. Supposedly opting for 11.5 over 10.5 gets you a little more dwell time in the cycling and a little more velocity and so some people opt for that extra inch. I personally like 11.5 or 12.5 to feel like I’ve got a lil’ bit more, but it’s probably not a huge advantage. I’ve not ever had problems with a 10.5.