Well I'm new to 3gun but I'm 20 years in LE with 16 in Tactical operations. I have banged steel, standard sized uspsa style out past 300 with a 12.5" on up to a 18". the one thing i teach new operators is the rifle is a tool and with any tool you should know what it will do when used properly. now i prefer a 14.5 pinned of most any type as i never have needed to shoot sub-MOA with a 5.56 anyway.
And I'm sure others have said this but it really depends on your environment. Here in Alabama much over 150 yards is a stretch for most matches, or so i hear.