I'm on my third 416 Rigby, had a 416 Taylor, 450 Ackley, several 458s and my double .470 NE, as well as my 50 BMG. I've fired everything up to a 4 bore double, including the 378 and 460 Wby, and a 50 cal on the 460 as well as a 50 cal on a rimless 577 NE case. I have several dislikes on the subject of the big Wbys, and Boomer hit on the biggest one, belt diameter vs magazine capacity. The 450 Rigby is a superior design for this reason, as is it's slightly smaller cousin the 450 RUM.
The boys of years past who were able to do significant ballistics testing on elephant and other super big dangerous game, determined the maximum impact velocity for a solid bullet to give the greatest straightline penetration to be no greater than 2400 fps. Weatherby used to advertise their 500 gn solid load at 2700 fps and several PHs found that load to not be reliable 100% of the time. When using a cartridge like this for back up and defense the impact velocity is virtually the muzzle velocity and on a steel jacketed lead cored solid, 2700 fps would almost tear it apart. A lot of riveting problems and bending problems as well as complete fracture issues, hence the new advertised velocity of the 460 Wby 500 gn solid of 2550 fps. It is still not favored by PHs because of it's previous reputation, as well as recoil recovery time. A 577 double can be recovered and the second shot aimed and fired before the same shooter even gets the 460 reloaded and recovered from recoil, a serious consideration when lives are at stake and one is hunting things that kill back. It is also my opinion that once you get into calibers of 45 and up you are no longer into multi purpose cartridges, but into specific duty guns and cartridges designed for "up close and personal" use. When using a gun as designed for this purpose, control and repeat shots are as much a concern as is raw power.
Don't get me wrong, the 378 and 460 Wbys are fun guns and will detach retinas if one tries too hard and shoots too many shots at a time, but the 460 really doesn't have a defined place in the hunting fields, kinda too much of a good thing. The 378 is really the ultimate medium as far as trajectory and hitting power goes but again suffers from 2 shot magazine capacity and does so little over the 375 RUM that one needn't sacrifice the 3 or 4 shot magazine to step up to the 378 over the 375 RUM.
I have just designed a cartridge based on the 416 Ruger necked out to 458 with the shoulder improved to 40 deg and moved slightly forward. Dave Kiff is making the reamer set as I type this and I have purchased a donor rifle in the form of an old Rem custom shop 700 in 458 WM, in beautiful condition. According to my calculations it will equal or exceed the 458 Lott without the belt and work through a 300 WM length action, without seating bullets too deep. I gave this reamer a significant throat length so as to use homogenous solids without sacrificing powder capacity. This should be IMHO the ultimate DG rifle (without entering the debate of PF vs CRF) and should drive 500 gn softs and solids at 2400 fps easily and at pressures that won't lock up the rifle in 55 deg heat as I have experienced in the game fields of Zambia.
The Rigby need no more applause than it has already, it is a very versatile medium and moves up to dangerous game very well, as well as using lighter bullets at velocities that make taking game out to 400 mtrs a very real possibility. I think every one should have at least 2 375 H&Hs and one 416 Rigby. Taylor wrote "the 416 Rigby kills elephant and other dangerous game all out of proportion to it's caliber and bullet weight, and is an excellent choice for a medium bore which may need to be used on dangerous game" not an exact quote but paraphrases his thoughts on the Rigby.