I built an 11.5" upper with a Bravo Company USA CHF barrel, Knights URX and BCM BCG. Anyway, while I am waiting on the paperwork it is on a pistol lower to test it out. It is surprising how fast it shoots.
Silver State Armory 77 SMK= 2489 average 5 rds
75 Horn. TAP (5.56)= 2506 average- 5 rds
Handloads of 24.6 TAC and 75 Hor.= 2519 average- 5 rds
This gives me exactly 2200 fps @ a range of 180 yards: so fragmentation range with the handloads and the T2 Hor. is pretty darn good for an 11.5" barrel
Anyway, I think a SBR with the right ammo can be very effective to a greater distance than some would think.