A bit of clarifying here.
First trust Wikipedia with a grain of salt.....in every regard not only firearms
Having said that, the 300 RUM is a higher performance cartridge compared to the 300 Wby...not much but definitely it has the edge.
Of the 3, the 300 Win Mag is at the bottom the pile...however the RUM and the Wby need longer barrels (minimum 26") to take full advantage of their superior ballistics.
If you want to read about the full capabilities of the 3 cartridges (and test barrel length for the various loads and different bullet weight) check the Hodgdon Reloads Data center here:
http://data.hodgdon.com/cartridge_load.asp
Or the VihtaVuori Reload Data Tables here:
http://www.lapua.com/fileadmin/user_upload/esitteet/VihtavuoriInternationalReloguide2009.pdf
In a 24" pipe, the 300 Win Mag and the 300 Wby are almost ballistic twins, with a longer barrel the Wby pulls ahead more
The 300 RUM, in turn, is outperformed by the 30-378 Wheatherby Magnum
One aspect to consider is that the 300 RUM is a very new cartridge and we do not know yet if is going to stick around for long....there is a slight chance that you may end up 10-15 years down the road with a rifle where the ammunition is almost impossible to find and/or outrageously expensive, however Remington is being smart about it and it is selling rifles chambered for the its super 300 Magnum at very competitive prices (for example compared to the almost equivalent 30-378) to create demand and gain staying power....we will see...
Overall, talking about hunting, there is nothing that the 300 magnums and super magnums can do that a 30-06 can't do more cheaply and with less suffering for your shoulder and ears....you gain just a bit of flatter trajectory and point blank range.
Punching paper (or killing BGs...but I do not think this is what you are interested in doing...) at extreme range is where the 300 Magnums really shine, however in that kind of application the platform (read: Rifle) and the optics are more important than the cartridge itself...
What I mean is don't assume that you buy your cheap Remington 700 300 RUM package deal at Cabela's for $549 and you can start punching paper accurately at 1000+ yards...is not going to happen....