I've found that trying to get a few extra fps out of a rifle doesn't pay the dividends one might anticipate. Usually all you get is more recoil, muzzle flash and shorter barrel life.
I only shoot 180 grain in a 30-06. I had a Remington 742 with a 22" barrel that would give me 2600 fps with factory loads. I developed a deer load that gave me 2471 fps. When I switched to a Remington 760 carbine with an 18 1/2 inch barrel, I still got 2470 fps with this load. I later developed a moose load that gives me 2630 fps in this gun.
I believe that if you increase your barrel length by two inches you could get anything from 20 to 100 fps more velocity (probably more like 50 fps), however, the advantages you might realize from this would be negligible, and not worth the cost.