There was recently another thread where a member was asking about 7-08 performance in an 18in barrel. Check it out here: 7mm08 help
If you can get a 140gr pill moving at 2600fps, you should hold over 1000 lbs of energy at 400 yds. I would guess that 2600fps is possible with a 16" barrel, but there is only one way to know for sure . . .