Big Boom AR

[MassMark]

So I'm back in the game...finally My AR-15 build is under way and though it will be starting life as a 5.56, I'm already plotting upper purchases - heck even more builds down the road. Some thoughts are 9mm, (I have a ton of it for the Uzi), .45ACP, (think it would be neat) and then I was thinking of a big bore upper and need some opinions. Is the .50 Beowulf a passing fancy in favor of the .458? Are they essentially 2 different animals? I have fired a Beowulf and was impressed - is it here to stay?

Thanks.