I've never been interested with any of the RUM cartridges but looking on here it seems the case water capacity is about 20 grains more than the Nosler Real Guns - Remington's Ultra Seven Magnum
According to that site the 7RUM can push a 140 grain bullet 3300-3400 fps or so. According to Bodington's article the Nosler 26 will do the same with 20 grains less case capacity. I'd think the larger bore of a 7mm Nosler might be even more efficient?
Again according to RealGuns the 7mm Rem Mag can send a 145 grain bullet around 3100 fps so you're not making huge gains in the lightest weight bullets going to the RUM or I would assume a 7mm Nosler.
I know the larger case capacity cartridges shine with heavy for caliber bullets just using the 140's as a comparison as that's what was shown in the article. I'd think a 7mm Nosler pushing a 180 grain Berger VLD would be just about the perfect rifle.