Re: Rate of twist
Every 300WM on Savages website I looked at listed a 1-10 twist, so you it sounds like your right on there.
What the rate of twist practically does is to limit how heavy of bullets you can shoot, for stabilization reasons. You can shoot light bullets in a slow twist or a fast twist, and while they may be slightly "overstabilized" this has no dramatic ramifications. Heavy bullets will only stabilize in a fast enough twist, if it is too slow, you won't stabilize them and accuracy will suffer, possibly severely.
If you have a faster twist than you need it could cost you some velocity compared to a barrel of slower twist, but this is a relatively minor effect, and normally only something to be considered if you know exactly what bullet or what range of bullets you plan on shooting when ordering a barrel.
With a 1-10 twist win mag you should be able to use pretty much any commercial bullets, up to and very likely including the 240 gr SMK's. So you don't have much to worry about regarding twist vs. bullet weight with your set up, assuming that you will stay within the readily available commercial bullets.
I should mention that velocity is also a factor in stabilization. The faster you drive a bullet the more likely it will stabilize for any given set of conditions. I have also heard that it is actually the bullets bearing surface length that matters and not its weight (they are inherently related) but I donít know much more than that.
Good luck and good shooting,
Empirical results rule!