It's hard to beat the 7mm Rem Mag. I won't hesitate to shoot at an elk 500 yards away conditions permitting with mine (I practice at a 600 yard range). The same is true with the 300 Win Mag, but the 7mm is a better all-around cartridge if you plan on shooting smaller animals like antelope in addition to elk.

All of the people who say you shouldn't be shooting farther than 200-300 yards have probably never hunted in the West. There's nothing unethical about it, and sometimes your freezer will be empty by the end of the hunting season if you're not willing to take that long shot.