Never owned a 7mmWBY or STW, but saw years ago that the WBY is certainly no slouch, especially the way Nosler loads it. Pretty close to the figures touted by handloaders for their STW rifles. I wouldn't have rechambered that rifle either.
I chronographed a tad over 3300 FPS(DOn't remember the exact number but do remember it exceeded factory specs) for a 150 grain BT out of a 7mm Weatherby (Factory Ammo) 26" barrel 80's Fibermark a few years back. It was a crap chronograph(Chrony) so there is that as well. That rifle was easily SUBMOA .
As to the 300 win mag vs 300 weatherby , there is not enough difference for an animal to notice IMHO. In the lack of recoil department the 300 win mag wins.
