Re: 300Win in a 40X.??
I'd say pass on the 40X, and get a Sendero instead.
I'd lusted after a 40XB-KS in .220 Swift since I was about 13. At 26 or so, I was in a position to get one NIB at a gunshow. The gun shot well (0.40-0.45" groups) w/ factory ammo, and sadly, not really any better w/ handloads. The barrel is a better grade than what normally gets screwed on your normal VS or Sendero. The actions are normally clip-slotted. The stock isn't just fiberglass, it's Kevlar. *Damn* hard to work w/ as far as reshaping or inletting for bedding, pillars, extending LOP, etc. They also have a blind magazine, ala Rem ADL style, which is damn annoying to me. I don't believe the actions are trued to any significant degree, rather I think they use a more select set of criteria for the 40X vs the 700.
Basically, in my mind, they are like a Corvette. Yes, they will work, really well in fact. But for the $$$ you tie up in what is essentially still a hopped up factory rig, vs. an all out custom job, you could be well on your way to a true custom rig. Of course, the same argument is made against any custom rifle built off a Remington action; I just feel the 40X represents an exceptionally poor value in terms of accuracy for $$$ spent, when compared to many 700VS, Senderos, and even Savage 12/112BTs.