257 Wby

Rl22 is a great powder for the 257wbymag but I stopped using it when I seen how much velocity drops in the cold. 7828 is easily a mach in speed and accuacy and doesn't lose the speed near as much.
I think it's tough to beat 7828ssc with what you're trying to do, but shooting an ELDx at Weatherby velocities, especially the 257, seems like asking an awful lot of the bullet. Unless you're really planning to stretch it out there, I'd recommend a mono. I prefer Hammers myself but have heard Barnes offers a really good one too. My Mark V shoots the 92gr HH at almost 3800fps with ES of 3 and stacks them into one hole. I think it's impossible to shoot a better bullet than Steve's creations for hunting, they do cost a little more but it's money saved when it comes to load work up. I load mine at 3.205''.
Good luck with whatever you decide. The 257 is a hell of a deer and coyote slayer!
7828 was my choice in the 257 wby. I used Speer 120 grain btsp. Tagged some big bodied bucks with that combo and never had to go look for my animal . Always a drt
The Barnes ttsx is a good one and the hammers get a good following too. I've never shot and animal with a hammer but Barnes a good at the velocity your going to get. I've killed a pile of deer with the 257wby the last 35yrs and it does a great job. Literally every deer but 2 dropped on the spot. The 2 that didn't only made it less than 20 yards. Superman deer because both had lung soup in their chest. You won't be disappointed 😉