Yes the 500a2 looks like a neat cartridge. I think very versatile when you can load to say 500 nitro levels all the way up to full power loads if you want to loosen your teeth.
To be honest haven't even been on a biggame hunt yet. My rifles tend to visit the range or accompany me on hunting trips where goats, pigs and deer are the target. I'm in the planning in going hunting some wild scrub bulls in Wanganui here in NZ with my Ruger 375HH. There's alot of satisfaction that comes with owning and shooting exotic or obscenely fun rifles. Do I need a large calibre rifle...nope...I'm sure a 308 with 180gr pills would deal to wild bulls. I think like a lot of people the "just want one" factor happens a lot.
Would the 585 Nyati be any harder to get to feed than a 500 jeffrey? We have an excellent gunsmith in NZ by the name of Allen Carr who has build several 500 jeffs that I would have in mind for the project.