Much depends on exactly what you want. I have both the .416 Rigby in a fancy-wood CZ, and the .416 Rem. Magnum, a custom M70 with Echols Legend McMillan stock. I use the .416 Rigby strictly with iron sights, and scope the .416 Remington. They weigh exactly the same, 9-1/4 pounds each, so the weight of a .416 Rigby depends to some extent on if you scope it. (This is also, by the way, exactly what Harry Selby's .416 Rigby weighs.)
The big reason to choose the Rigby, aside from romance, is pressure. I know several PH's who report very stocky bolt lifts in hot weather from the .416 Remington in factory ammo or equivalent handloads. In most weather it works fine, however. the Rigby never has any such problems.
I have had two 1-shot kills with the Rigby on shoulder-shot buffalo so my experience is a little different than that of others here. I have hunted a little with the .458 Lott but have found the .416's so satisfactory that I don't feel the need for anything bigger. The 416's are a noticeable step up from the .375.
If you want an opinion on whether the .416 Weatherby (or any other round) is the greatest buffalo cartridge ever, I would ask Craig Boddington. He is the only American gun writer who has killed a LOT of buffalo, with a wide variety of cartridges. Most writers have killed maybe half a dozen, but then again anybody who has ever killed one Cape buffalo (or maybe even none) is ready with an opinion on suitable rifles.
