For a max of 400 yards, I would still prefer the greater horsepower of the 280AI over the 7-08 for elk.
I took your MV for the 140 Berger and ran it through my ballistic app and you have right at 2081 at 400 yards with the Berger.
Even though the 140 AB I have has a lower BC, my impact velocity at at 400 with the 280AI is 2214.
Just some numbers for you to consider as you make your decisions.