You cant really be serious if you are trying to compare 450 to 300blk, the performance and uses is on a whole other level.
There is more to a cartridge than just knock down power.
Sure, the 450 Bushmaster has way more stopping power but if I'm going bear or moose hunting I'll just take a more suitable rifle out of my safe like my 45-70 or my 338 Lapua.
For every day shooting the 450 Bushmaster is a poor choice. The cost of ammo is insane if you don't handload, and the recoil and punishment the firearm takes is unnecessary. Remember, these rifles were designed to run 223, it would be the same as putting a Corvette motor in your civic, fun in the beginning but it just starts breaking everything around it.
The 450 is a great cartridge and I wouldn't mind building a conversion for my ACR just for hunting season but it isn't something I would want in a rifle like this full time. I like to shoot my rifles regularly and the 450 will probably end up breaking the rifle after a couple thousand rounds.