I agree with bialey...I'm having a 300RUM built as I type (my obvious chioce of the two)but if you are going to go with the big case, go with big bullets. I found this board when I was asking, why the RUM when you only get a couple hundred fps over the WM with 180gr bullets? If you want to use the 180s & 150s you might want to think about a WinMag (or heaven forbid, the 7) and save the powder, barrel and recoil.
Either way you will do good, good luck.
Genises 27-3: Now therefore take, I pray thee, thy weapons, thy quiver and thy bow, and go out to the field, and take me some venison...