A few things to consider when choosing a cartridge and loads.

Firstly,most guns will not shoot the full range of available bullet weights accurately.In other words if you buy one of the cartridges that uses a .308" bullet,don't expect it to shoot all weights from 110gr to 220gr accurately.The reason for this is that the rate of twist of the rifling can't be optimum for such a large variation in bullets.Usually the best accuracy is obtained within a given range usually from 150gr to 180gr or perhaps 165gr to 200gr in .308".In 7mm the optimum accuracy range is usually 120gr to 160gr or 140gr to 175gr.Of course these ranges do vary from rifle to rifle and bullet to bullet.

Concerning the accelerators used to fire .223" bullets in barrels designed for .308"bullets;accuracy is very inconsistant.Some guns shoot them reasonably well but they they shoot patterns rather than groups in many rifles.

Switching bullets or loads back and forth when hunting different animals does have it's drawbacks.Since it is common for different bullets to shoot to different points of aim you must recheck the point of impact whenever you change loads.Secondly,different loads have different trajectories which means that you must learn more than one trajectory and must always be aware of the trajectory for the load that you are using which can cause problems when buck fever kicks in.I have witnessed this situation myself in hunting situations.A good way to prevent these problems is to select one load suitable for all of you big game hunting that shoots accurately in your gun.Then you need only have one sight in and one trajectory to remember.Simpler means less chance of a mistake and a missed or wounded animal.