I'm a happy owner. I spent a lot of time digging into the big bore cartridges before I took the plunge. I settled on the 450bm because it was the only SAAMI recognized round, you can buy ammo and reloading components easily, and the bullets could be used for my .45ACP reloading.
The Beowulf looked interesting but have to pay huge price on gunbroker for ammo and components; ditto for the .458SOCOM. With Hornandy and now Remington making ammo, its simple to find 450bm almost anywhere online, and even in gun shops.
All three replicate the 45-70 so "power" isn't an issue. But I like I can load up the same 230FMJs I use in my .45ACP in the 450bm but with fps in the 2500 to 2700+ range. Yee hah, that'll solve any zombie problem!
@ Welding Rod and others: You can use stock GI mags, but you need to either install a single shot follower or simply take a dremel to the standard follower and grind it down to look like a single shot. Wa lah, fully functional magazine.
There is a bunch of load data, tips, tricks, etc at
450bm.com
and a discussion forum is here:
450bushmaster.net
Good luck with your shopping