The way I see it, the difference is about 13 gr of water capacity. About 11 if you use commercial 30-06 brass.
If you only buy factory ammo, the 300 WSM is a solid 200-300 fps ahead of the 30-06.
If you handload, and aren't averse to warming up the 30-06 a bit, then the 30-06 is only about 100-150 fps behind the 300 WSM.
Remember the 300 WSM is loaded to around 65K lbs-psi. The 30-06 is loaded to around 58K.
I typically load my 30-06 to around 62K or so, as interpreted via a chronograph, and Quickload velocity/pressure correlations.
A lot of folks poo-poo that approach as hazardous, yet they may not consider that 65K is SAAMI standard for such rounds as the 270 Win, and 25-06 Rem.
As far as action length and magazine capacity goes, that's mostly personal preference. There are always aftermarket DBM systems to increase capacity. I don't see any great advantage to the short action over the long myself. I kinda favor the Remmy long action magazine for the latitude it offers in oal.
