I would stick to the more modern or improved cartridges because they have the faster twist rates that will run any bullet like the heaviest solid copper bullets, and they tend to have the right size magazine lengths without a silly belt or the bullets seated way down in the case like the 300WM for example. The reason that's important to me is that I believe in tough bullets for elk and bear. I know there are many people here who like the Bergers and other cup and core even match bullets but I never was a follower. If you want to stabilize a 210 Barnes solid for elk, you won't do it with any of the old caliber unless you change the barrel for a 1/8 twist, which my 300PRC came with. I like the Barnes for elk. For deer, cup bullets are fine most of the time but elk at long range sooner or later you'll lose one. Anyways, I sold my 300WM but kept the 300PRC and never looked back. Also, I'm continually perplexed by the "you can find ammo anywhere" statement that keeps coming up for all the old calibers. Why would you want to? I hunted for 50 years straight and never once forgot or lost my ammo. I also have never found a single box of ammo over the counter that out-shot my handloads that I tailored for any of my rifles. Some boxes were acceptable to 400-500 yards maybe, but none had any business getting launched at game at long range. In other words, you are not going to win a thousand yard rifle competition with factory ammo unless you are by yourself. As to the question the OP asked, I was going to say 300 PRC and 7mm PRC until I heard about velocity issues I haven't looked into that yet (7PRC). I've heard all the arguments and this is my opinion, which you asked for and that's all it is. I will add that I went to the 300s for elk because I wanted more power and range than my .270 could give (yes under powered). I passed on the 7mm RM. For an all rounder single caliber I would probably go with the 7 PRC, 26", with no brake. I still carry the .270 for deer. Anyways, don't anyone blow a gasket, and have a nice day.