I hand loaded a 300 Weatherby for several years as a favor to a hunting buddy-Strictly 180 grain Nosler partitions on top of a ton of IMR7828, Fed215M primers. I whacked a California mule deer doe off Tejon Ranch with one at a paced 317 and I coulda seen Nevada through the wound channel.
I believe it is the perfect elk gun out to probably 400 yards. There are many choices though and as usual, bullet placement will let an inferior caliber do just fine. Problem is, a quartering away 6x6 at 350 yards needs some T H U M P. And of course you need to do your part so be sure whatever you settle on you can de-sex a flea at all yardages.