Re: 300 rum
The 300 RUM has been my go to for the last several years. I don't think it can be beat for versatility 130gr TTSX for a screaming fast whitetail grenade, to 210gr VLDs for long range work. I have stuck with 168 TSX and TTSX. It shoots flat as all get out and hits hard. it has been a fantastic killer of big game.
If I was going to setup a dedicated long range rig I would look really hard at those Nosler Accubond LRs. It has tremendous potential for a true long range power house.
Did you go with an extended magazine box? If not you might want to consider it, especially if you shoot any of the VLD type bullets that like to be loaded out to the lands. Like berger hunting VLDs. Wyatt makes a good one that is pretty easy to install that gets you out near to 4" OAL.
Congrats on your rifle, looks like it will be a good shooter.