Today I shot the last five rounds of steel case that my 14.5" Super Duty wouldn't cycle until I put in a PSA std weight carbine buffer and spring. I saved it until today, because my magneetospeed sporter came in this week. I got some velocities from different loads I use for different things, for comparison and so I can have really good holds on long 2-gun stages.
Results (All from the same 14.5" SD rifle with a round count around 2k):
Frontier FR320 (75 gr): 2615, 2637, 2645
Frontier FR310 (68 gr): 2756, 2752, 2713, 2774, 2795
Norma Tac .223 (55 gr): 2892, 2897, 2914
IMI "M193": 3011, 2960, 2949, 2946, 2936
Red Army Standard .223 55 gr FMJ: 2693, 2701, 2716, 2727, 2722
So, basically, about 200 fps slower than non-garbage .223 or 300 fps slower than 5.56 with same bullet weight, and still ~50 fps slower than match 5.56 with a 13 gr heavier bullet in a load that is optimized for a much longer barrel.