You're on the right track alreDy with a 700 action. I am not particularly a big fan of either caliber, even though I have become quite good at reloading 300 WinMag since one of my best friends has one, and we have done alot of load progression.
If you reload, hard to find ammo will not be so hard to find once you buy brass & dies. For example, the 7mmSTW is one of the best long range calibers, but it not as popular as it used to be. It is one excellent caliber for long range huntjng and shooting.
But 300 WinMag is also a great caliber. But it's a little too mainstream for me. I like going against the grain. LOL