Re: Dangerous game rifle: CZ550 / Winchester M70???
If you don't reload, I don't really think there is a dime's worth of difference between the cartridges. I have heard good things about the .416 Ruger. A good friend of mine took a very nice Cape Buffalo in Zimbabwe last year with one. I don't personally have experience with the .416's so I can't offer any first hand advice on them.
In theory, the higher pressure cartridges can encounter extraction problems in hot climates. I know both the .416 Remington and .458 Win Mag had a bad reputation in Africa because of reliability problems associated with high chamber pressure (also because of poor bullet performance). That was a long time ago. Factory ammo quality has improved considerably and the powders in common use today tend to be more temp stable.
I wouldn't really worry myself about rated chamber pressure. I would expect the Rigby to have greater overall potential than the other two, but that only really counts if you handload. Failing that, I would really just go with the rifle you like best, buy ammo for it, and start shooting/hunting.
The Ruger, CZ, and Winchester are all reliable controlled feed actions. I don't think you can make a bad choice among them.
The CZ is heavier, but very well balanced. I consider it to be more feature packed than the other two. That is only relevant if you like the additional features, though.
The .416 Ruger is more capable of max performance from a short barrel vs the other .416's. If you want a shorter, lighter, faster handling rifle, I would expect the Ruger to edge the other two out.
The Winchester is a timeless classic that, in my mind, would sit somewhere between the other two in terms of weight and handling characteristics.
My personal bias is toward the CZ, but that is because I like the features offered and I prefer the addtional weight, length, and balance of a true Magnum length rifle. I find its bulk somehow reassuring. Not everyone feels that way.
Truthfully, I can't really say that one of the three is better than the other. The difference is really in which set of tradeoffs suit you best.