The 338 Edge will carry out there for sure.
It's going to carry a hefty price tag too if their custom 308 win price is any indicator.
Check out this site for scope rings and base:
http://www.badgerordnance.com/ They have good stuff.
I think the 8.5-25 M4 has 72" of travel overall, not just from optical center. Could be wrong about that though.