this is just my personal thoughts on the matter but...
300 BLK has almost no ballistic advantage over the much cheaper and more readily available 7.62x39. however if both are in an AR platform rifle the 300 BLK is a more reliable choice as it takes standard magazines, BCG, buffer everything, the only thing you need is a new barrel. 308 also offers a wider range of bullets to load but cost is still pretty steep and availability, though getting better, is still pretty low.
458 socom is pretty much a rimless 45/60. great deer smacker at close range but not a lot of practical application past 200 yards.
ignore my complete lack of capitalization. I still have no problem correcting your grammar.
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