I got a new MRX last year after struggling with an older muzzleloader for a couple season before that and bad luck with the CVA bullets.
My MRX loves the 290 FTXs and 100gr of 209 by volume. I wish some of my centerfires shot that well actually.
After using it on a couple of deer, I'm still not 100% impressed with it. Talking all 100yds and in. Bullet seems to go straight through and doesn't leave much in the way of a blood trail. Actually the last one I shot I would have swore I missed it if it didn't jump up on its hind legs like a horse. There was absolutely no blood for 100yds until I found it piled up in some thick woods. This is the same problem I had the year before with CVA ammo.
I'm no expert in MZ ammo but thinking of trying the Barnes expander HP next year. Most of my shots will be under 100yds so the BC shouldn't matter. Maybe I need to change my shot placement too. I hate to waste meat but ruining a shoulder is better than not finding an animal.
All of my experience is on deer so don't let that detur you from your bullet choice on elk.