I know the OP mentioned a custom 7mm Rem but he failed to mention the length and twist of the barrel. All very important info in order to give him a good bullet recommendation...
All high BC copper bullets will require faster twists.
Now if the OP is running a 1:8 twist and a 26" barrel, I would recommend the Hammer 177. IF.... he can push it at 2900fps from the barrel and uses a minimum speed of 2000 fps for the bottom terminal speed, then he will be good to 650 yards at sea level and 850 yards at 4000 feet. The more common 9 twist would likely force him to use a lighter and lower BC bullet that likely won't meet his goals for elk at 700+ yards.