I'm sure that the 06 with a good 200gr bullet, ie partition, tsx, or aframe, would work just fine. I don't see the 325 wsm as that great a step up in power over the 300 magnums. A 300 mag, either wm or wsm, would also work just fine with the 200gr bullet just as well as the 325. I honestly think you would be better served with a 300 over the 325.
Stepping up to something like a 338 wm/338-06 or 35 whelen/350 rem mag are another ball game. They do offer some real increases in thump over the 06 or 300 mags. THey offer bullet weights up to 250+ grs and would be just as at home in montana chasing muleys and elk. Also now that the montana is going to be available in full length cartridges a 300 or 338 win mag would be a really nice rifle, especially if mated to a good compact scope like a leupold 2-8x36.