the 416 Rigby in a CZ 550 is a fine choice but you can expect the CZ 550 to need a little work before it runs perfectly. also, if ammunition price is a concern then 416 Rigby may not be the best choice as its certainly not cheap.
for a first time buyer i would actually recommend the Winchester M70 in 416 RM. the 416 RM cartridge is fantastic and is much more cost effective then the 416 Rigby cartridge. the Winchester M70 rifle tends to run only slightly more then the CZ 550 but is a much nicer rifle out of the box (the CZ can get there with work).
in summery, any of the 416 cartridges will serve you well for both DG and PG.
my thoughts as per my post as well .