54x50 is fantastic with a 1-28 or faster twist. The 50-275gr Barnes XPB or ML bullet is plain nasty even at mild speeds. Heavy loads of BH209 and good 300gr+ bullets would likely kill anything in North America humanely. The Rem 50-385gr CLHP is very impressive if you want max knock down from a 54x50 and a higher BC.

This year i tried the 458 300gr SOCOM in a Harvester sabot and its becoming my favorite. IMO it turned a brush gun into a potential 200yard gun with less hold over and reasonable recoil in a small package.

Given the choice i would choose the 54 but not because of component availability. The only 54cal sabots i can find locally are the 54x45s from Harvester at Grafs. Knight is just a phone call away for 52cal sabots and they work fine. Rumor has it that Harvester might even offer a 52cal sabot soon too, possibly in 52x452 which will give you a ton of bullet options.