Well, a standard long action will be smaller and lighter for a hunting gun. Just a small consideration. They both shoot 230s in the 3000 range so once it leaves the barrel it's not much different. Reloading and rifle build costs will be much cheaper with the RUM too.
P.S This is all coming from someone who wants a 300 Norma.
Oh, and this current deal may be interesting to you too. $1900 for a Mausingfield barreled action, even in 300NM. It says long action is sold out but I think they still have some as you can choose it in the drop downs (You couldn't choose it a couple days ago).