My 308 BLR has a 20" barrel, it's killed lots of deer and elk exclusivley with 180gr pointy bullets, PSP Core-lokts and Failsafes, I don't think another 1½" off the barrel would make a lot of difference to any critter, big or small, go for it, that'll get ya one gun closer!!
I've never chrono'd it, don't really need to, do I!!
Tim