Looking at the major pluses and minuses, I'm sure I missed some.
The 300 WIN is definitely a great travel cartridge like some others 30-06, 270 WIN, 243 WIN, 308 WIN, 375 H&H etc. as far as ammo being available at the local gun store whether its in South Africa or Rifle Colorado. And typically cases are available from most retailers. The SAAMI length does not support long high BC bullets. You can load them but they will extend into the powder space to fit into the mag.. The case maintains the legacy belt portion, not a huge deal but its there.
The 30 Nosler gets rid of the belt, not a huge deal but it does, and has the same SAAMI length issue the 300 WIN does. The components ie. cases are higher in price than most. The SAAMI length does not support long high BC bullets. You can load them but they will extend into the powder space to fit into the mag.
The 300 Ultra has great acceptance in the US and you can likely find ammo at some gun stores. It also gets rid of the belt, not a huge deal but it does. The SAAMI length does not support long high BC bullets. You can load them but they will extend into the powder space to fit into the mag. It is known as a barrel burner and known to be tough to accurize some times. I cannot speak directly to these issues but they have been discussed ad nauseam.
The 300 PRC is the new kid on the block. Has a SAAMI spec length for long high BC bullets which means the magazines have to match the longer length and off the shelf ammo plus hand loads can take advantage of this feature. It also gets rid of the belt, not a huge deal but it does. Cases and loaded ammo are short in supply, but so is freaking everything right now. Sportsman's in AZ is out of everything, including 300 WIN.
The other "wildcat" 30s will mostly perform in the higher end of the ballistics range but all have the same issue I have with my 7mm LRM, small source choice for cases and higher than normal case price. I love my LRMs performance and hate it for the case issue. And if you think 300 PRC might be hard to find in Johannesburg then ... ;-)
In general if they are loaded similarly, ie. bullet base not past the neck should junction the performance between the 300 WIN, 30 Nos, 300 Ultra, and 300 PRC will be so close no critter will ever notice at normal hunting ranges. The wildcats will always be a little higher, performance wise, but still not a huge difference really. With all the ways to get range and correction for elevation super duper velocity performance is really a mute point these days. Higher BC + higher velocity will help cut wind deflection and can make some differences at extended ranges on smaller targets making wind call mistakes mean a little less. But, should you be shooting in high wind at extended ranges at flesh, blood and bone, I don't but maybe you would so do the math and look at the wind deflections, its the hardest thing to deal with by far.
So I think someone said early what are you looking for? A toy or a tool. What's important to you? Do you want or need the ammo availability of the 300 WIN? Do you want to shoot high BC bullets for better long range performance and like the SAAMI advantage of the PRC? The longer lead can obviously be achieved by and custom chambered rifle in any cartridge as the lead can be customized for any bullet as well as the choice of magazine you just may have poorer results from factory SAAMI ammo. If you have it in your head that you need to shoot the fastest thing going then you need to be a hand loader and pick one of the big wildcat 30s.
Personally if I was building a travel rifle I'd chose a 7mm REM Mag with an extended mag and extended lead length to maximize case space. It has reasonable recoil and all the ammo advantages of the 300 WIN with a huge choice of of high BC bullets to choose from. I like 7s so sue me. That was fun.
