A 7mm bullet is a 7mm bullet no matter what rifle it is shot out of, be it a 7-08 or a 7 RUM. The difference is the velocity it has when it leaves the muzzle. many of the members of this site consider minimum expasion velocity the determing factor in a cartridge and bullet's kill range. Many also use 1500 ftlbs of energy as their minumum on elk. I look at the bullet's minimum expansion velocity for the most part and also look for about 40 lb ft of momentum for penetration on elk. For a long range shot on elk with a 7mm I would recommend being selective with your shot. My first choices of bullets for the 7-08 would be the 150 E-Tips and the 160 AB's. RL17 is a good powder for the 7-08 and can get you some more performance over other powders. With a good load you could take an elk at well over 500 yds with a 7-08
The 7mm isn't the best elk killer, but if it's what you have, use it wisely and it will get the job done. Wouldn't hurt to be ready with a follow up shot and above all, try not to spook the elk.
Good hunitng,
Mark