Well, I think ol' Roy is wrong, at least regarding DG calibers. Velocity is helpful when looking at external ballistics (bullet drop, wind effects, etc. - which are almost never a factor at the ranges that DG are commonly shot), but can become detrimental when the bullet meets animal. If my 400 grain 404J bullet fired at 2250 fps can fully penetrate a buffalo at 100 yards and kill it within seconds, what do I gain with 2700 fps? The bullet will open faster and this will impede penetration. Greater recoil makes it more difficult to shoot accurately.
Roy is puffing his proprietary cartridges to make sales. OK with me, but I don't find it convincing in this case.
I've written about this on many threads on this forum and indeed, Roy's ideas are as much religion as they are science. What we do know are three truths, but when adapted to other calibers the truths don't always transfer over.
1.) Truth 1. Heavy for caliber, long bullets, at moderate velocities, create a long "hang time" in the animal and can have devastating effect. The very best example of this would be 6.5x55 Swede (and 6.5 Mannlicher) or the 7x57mm / 275 Rigby. They were braining elephant with these rounds and the Euros were killing moose with heart shots with the these rounds. These soft-recoil rounds prove this truth.
2.) Truth 2. ANY gun of 40 caliber or greater that can send 400gr bullets at a muzzle velocity of 2150fps and an impact velocity of 1900fps will kill the largest animals on the planet. This is why the 404 Jeff and the 450-400NE are so beloved. They are super mild recoiling versions of this truth. A 470NE, 500NE, or a 500 Jeff are just extra "insurance" that allows this truth to be realized with a 500gr to 570gr bullet.
3.) Truth 3. Speed kills. If you take a tiny enough caliber to make it pleasant to shoot and you move it at tremendous velocity with a bullet that can maintain its structural integrity, the gas bubble around that bullet will cause enough sheer and hydrostatic shock to kill remarkable things. Roy Weatherby figured this out and its why the 257 Weatherby was a favorite for 600lb tigers and the 270 Weatherby is treasured by many elk hunters. It is manageable recoil pushing a tremendous hydrostatic gas bubble that causes an instant stroke in animals as the gas bubble reverses the arterial flow and causes a stroke or aneurism immediately.
The problem with ol' Roy is his entire business rested on truth #3 which he inferred was a constant truth that could just increase with heavier and heavier bullets. I do not believe his inference was correct because buffalo, elephant, hippo, and rhino are so large that you are not getting the same ratio of hydrostatic shock on the gigantic stuff (velocity x bullet weight x mass of the animal) that he was when using that logic on tigers, pronghorns, or elk. The other thing at issue was once Roy created this mindset and made gigantic calibers, the recoil was so fierce he had to bastardize stock designs that had been proven for nearly 150 years to a reverse drop comb or parallel comb in order to protect your face from the recoil effects.
My comments above do not mean I hate every gun Roy invented nor that I hate 460 Weatherby, only an opinion of what the real "truth" was and that it may have been misapplied from one subject to the next.