We have a couple of things in common, like serving under Pres Reagan and taking a break from hunting and shooting, and I am new to the LR game myself but have learned a whole lot in the last year and a half that I've been hanging around this site. First thing I would recommend is dont make any quick decisions. You may learn a few things over a few months that may affect your decision making.
On which 300 rifle you want, I think that depends on what you want to do with it. The 300 WSM
and WM are very close, and I'll have to take a little exception with my friend Tank. I developed a load in my 24"300 WSM with RL17 that will out run most 26" WM loads. In most cases the WM does have a slight edge on the WSM. But with RL17 I can get 2900 fps with a 210 Berger and 3160 with 180 E-Tips. One of the big advantages of the WSM is you can expect maybe double or more the barrel life. And I have this irrational dislike of useless belts on brass. Call me crazy.
On the RUM, I just got a used Sendero and am in the process of barrel break-in and load development. I am treating it with a product call Gun Juice which is supposed to lay down a lubricating protective layer that resists corrosion, increases barrel life and increases velocity. I *appears* to have increased velocity a little in my 25-06 Sendero and I am getting very good velocities with several powder/bullet combos in my RUM. I'll be posting a thread on my initial results and findings, probably in a couple of weeks.
I shot 30 rounds out of my RUM the other day in load development in about an hour and a half. It was a cool breezy day, good for cooling the barrel. There is no brake on it. I could have easily shot 30 or 60 more. I use a slip on recoil pad on the bench and it does a great job of dampening the recoil. A lot of guys in the LR game use brakes, mostly to be able to see their bullet impact and that's a great bennifit. I personnaly dont like them because they are extremely loud and are an encuberance on the end of my barrel. My rifles are all carry rifles and I am a walking, spotting kind of hunter. So in the field, the brake causes me a couple of problems by being a snag on brush and required hearing protection. if you ever shoot a braked RUM without ear protection you will likely never do it again. So, depending on YOUR priorities and hunting style you can make that choice. If I had a dedicated bench gun, and/or my hunting style was setup-ambush, I would definitely consider a brake.
The RUM will gain you about 300-400 fps over the WM or WSM, which translates to about 200-300 yds more range, depnding on your loads and rifle. It also uses up a whole lot more powder. With 67.5 gr of RL17 I can get 3160 with a 180 bullet and with 98 gr of Retumbo I can get 3440 with the same bullet. So the real question is, what do YOU want to accomplish?
I'll offer a prayer for your service to the Lord.
Be blessed and good shooting,