Well the 300 will certainly do the job at 600 yds, however you'll be taking more of a beating than you need to.
If you truely intend to stay inside 600 yds you can get it done with a 260, 7-08, 308. If you think you'll be stretching things after a while then you may want to look at the .270, 30-06, or the 270/7mm WSMs. All of these will be kinder to the shoulder than the 300WM.
On the other hand, if you really want the 300, by all means get one.