I am a big fan of the 338-06 and would suggest going that route. If you want a 20" barrel, get one. Velocity loss would not be an issue. I would be more concerned with muzzle blast, which the suppressor will take care of. I have loaded the 338-06 up and down in bullet weights and velocities. I have even messed with subsonic loads, but have not been happy with the those results. The suppressor makes it even easier to shoot.
I got a couple of 338 Federals to play with. Have not had enough time to form any serious opinions on the cartridge yet. One of main goals is to work up a subsonic load.
