I've never had or handled one but from all reports, the CZ 550 is supposed to be a very good rifle. When I got the model 70 pictured earlier, at that time I already had a CZ 602. The 602 appeared to be well made and shot well but didn't seem to be as nicely finished off as the model 70,

so I kept the pretty one

. If you had an inclination to go to a 458 Lott, the 602 action is easily lengthy enough to handle that cartridge conversion.
Nothing shabby about a classic like the 416 Rigby and there's also a few others in that calibre line up that

look 'interesting'. I don't know that I'd ever make use of something like that but I wouldn't mind playing with one. In reality, there's enough in my cabnet to keep me occupied as is.
There doesn't seem to be all that much difference between the 416 Rigby and the 416 Rem. Mag. so unless you were definately favouring a 'classic', the Rem. might be a good option. Graylake on site has a Rem. in a model 70 that he took to Africa a few years ago and from some of his last posts, it sounds like he was considering parting with it. If he still is, that may be an option.