I stopped at the range today and chronographed a couple of rounds of Lapua VPT 58 in my Glock 17L.The temperature was close to 60 degrees F and my chronograph was 10 ft from my muzzle.
The velocity was 1223 and 1233 fps,so I don't think my recollection of 1275 fps was very far off if at all because the 1275 fps was in the heat of the day in the summer probally 90 degrees F or more and the chronograph screens a couple of feet from the muzzle.
I just checked a few rounds out of a couple of boxes of ammo for overall length and it varied from 1.159" to 1.1635".
A link for velocities from a 4" barrel concerning vest threat levels.
http://www.geocities.com/jimandpetalawrie/NIJ-TL.html
THREAT LEVEL II Barrel Length (inches) Velocity fps Velocity mps
.41 Mag. 210 Grain SP 4 1300 397
.44 Mag. 240 Grain SJSP 4 1180 360
.44 Mag. 240 Grain Lead 4 1200 366
.357 Mag. 125 Grain JHP 4 1450 442
.357 Mag. 110 Grain JHP 4 1550 473
.357 Mag. 158 Grain JSP 6 1395 425
.357 Mag. 158 Grain JSP-Hornady 6 1445 441
.357 Mag. 158 Grain Lead 8 3/8 1410 430
9MM 124 Grain FMJ 5 1175 358
9MM Lapua 123 Grain FMC 4 1200 366
9MM Norma 116 Grain FMJ 4 1150 351
9MM Geco 123 Grain GMC 4 1200 366
9MM Canadian 116 5 1250 381
9MM Israli 4 1200 366
9MM Cavim-FMJ 4 1110 339