You realize you're dealing in hundreds of inches of drop at 1200 yards, right?
That means scope adjustment... sitting there and counting 400 or more clicks of a quarter-minute scope turret to go from a 100 yard zero to a 1200 yard zero?
A quick defensive-use rifle for dangerous game will typically not have a scope at all on it. It also will be a double-rifle of some sort rather than a bolt action, to avoid a terrible situation where a frantic attempt at extraction/ejection leaves the case rim torn and the cartridge still in the chamber.
Stopping big dangerous game is a job for a bullet with a blunt nose/wide meplat and a lot of weight.
1000+ yard marksmanship is a job for .24 to .28 caliber bullets with streamlined bodies, high ballistic coefficient and specially designed noses that are typically hollowpoints to aid in flight.
You're talking about two extremely different rifles and you're not going to get one that does both with any sense of authority.
In my safe... were I to shoot at blue helmeted zombies at 1000 yards (and I have zero practice at 1000 under my belt right now... my max tried is 300 yards), I'd go with my M14 and hope for the best with the "click" formula of 3/3/4/4/5/6/6/8/8 to get my iron sights out to 1000 yards from a 100 yard zero. I'm still likely to be off by at least a couple feet, though.
However, were I in large predator or manstomper country, I'd be carrying my .450 Marlin levergun (and wishing for a .458 WinMag and years of practice prior). Big, heavy bullets with a wide face that crush anything in its path.
That .450 Marlin will not make it to 1000 yards with near the efficiency of the M14 in .308.
