Both are reloader's cartridges. I have the 7 SAUM and the 300 and both are tack drivers. I have never bought a box of factory ammo for either, but I have long stated that if Remington wanted to make the cartridges a success they would sell the ammo for the same price as 30-06.
I bought the 300 M7 from Cabela's on the sales rack for $399 less $100 in Cabela's bucks, how could I go wrong. My load workups for the 7mm consisted of using H4350 and just about any bullet I can stuff in it for great accuracy. I did shoot two coyotes last year with it using 120 grain NBT's. The frontal shot worked out pretty well, that fur is still in the shed, the second was an ugly mess (side shot), so I went back to the 22-250.
I think the 7mm RUM is hideously overbore and would recommend getting closer to the game instead of stretching out the shot. Painful to shoot as well.