Depends on what you intend to use the rifle for. If it is a do all rifle then 2.5-16 is more useful than 6.5-20. However, if it is a range/varmint only rifle then I would say keep the viper as a little extra mag is always handy.
Of the two, I would prob keep the Bushy, as I do not like high mag hunting scopes. I prefer a wide field of view, especially on moving game.
As for the mil/moa turrets, if this rifle is used primarily for hunting, just work your dope this summer, then a week before your hunt input the environmentals to your ballistic program and then make a turret tape. You can still range with the retical, then dial for yardage. Very simple and easy to do. If you change hunting areas, make another tape. You can use white electrical tape, or print one using word, it takes a little trial and error to match the numbers with the dial but not impossible.
That was kinda my thinking. I don't mind mismatched turrets with the reticle in the second focal plane. I just adjust magnification accordingly and run it as an MOA scope. The vortex warranty is rock solid but I'm going to keep the Bushy.