I think you're talking minor velocity differences when you discuss one or two inches of barrel length. Stating the obvious, when you start comparing a 24 inch barrel to an 18 inch barrel then you have to start making decisions on how much velocity difference you're willing to accept or attain. This thread is already a classic example of different strokes for different folks. To me, 22 inches is about the sweet spot for a 7mm-08. As this is the Long Range Hunting sub-forum, if I were building for that stated purpose, I would think the 24 inch barrel would be my preference if that were my allocated use; however, 22 inches would work for me in that scenario.
