As of course you are aware, .25 MOA would be 2.5" at 1000 yards. Accepting .5 MOA (5 ") at 1000 is "more" realistic...but, if you look at the groups shot at most 1000 yard matches (regardless of allowed cartridges), very few shooters group five shots that close with any consistency. Five inches will take a good rifle and a good shooter and good conditions - at 1000 yards.
The variety of uses you describe suggests (to me) that you look at multiple rifles.
1. Long range competitions on steel - I suggest you contact the ranges that allow 50 BMG (see my Ranges page
- pink info re 50 BMG). Many that do allow 50 BMG will not let 50 BMG shooters shoot their steel. Alliance and Thunder Valley are the only 1000 yard ranges I know of in OH that allow 50 BMG. However, Alliance appears to limit 50 BMG to 600 yards and makes no mention of shooting on steel (at all). Thunder Valley shoots steel out to 1 mile. Call Tom Sarver if you can shoot his steel with a 50 BMG.
2. Shoot as far as possible - you would be better served with a 375 CT, 375 VM2, 375 Allen Mag, etc. It would be hard to find anyone that can show you evidence that a 50 BMG will out shoot those cartridges at ELR. That noted, the 50 BMG was designed to reach out there. Just not the "best" solution.
3. Portability - while that is "relative", most 50s are substantially heavier than 375 CT class rifles.
4. Hunting - with the correct projectile, "fit" ranges from very doable to overkill. 50 BMG in Africa? I suspect it has been done, but it is clearly not a preferred cartridge.
5. Suppressors - availability good, see that section on my Rifle Components page
. Issues are cost and bulk for such a large cartridge. Very doable.
6. Pleasant to shoot - beyond the noise level (dealt with by the suppressor - where they are allowed for hunting), the weight of the rifle has a major bearing. As the weight goes down (for portability) the impact on recoil suppression becomes more of an issue.
In my mind I don't see what you are looking for in any "factory" rifle (too heavy). While a custom is possible, it seems more likely (IMHO, most optimal) at three rifles:
a. An African hunter in an African cartridge.
b. A 375 CT/AM/VM2 class for ELR
c. A high end 50 BMG "factory" rifle for none of your stated purposes, simply "fun" (which was not mentioned)...and ego satisfaction.
Enjoy and God Bless!