So I've selected two companies with 4 potential loads for my elk hunt this year.  First time out with the big boy.  The selections are:

XCaliber Ammunition 300gr JHP(Hornady AMP bullet) @2000 fps
XCaliber Ammunition 45/70 Government 325gr. Brass Monolithic @1911fps
LeHigh Defense 45-70 Government 305gr Xtreme Penetrator @2,000fps
LeHigh Defense 45-70 Government 305gr Controlled Fracturing @2,000fps

XCaliber makes a JHP load of the same but at 2200 fps, but it practically takes my shoulder off.  I chose these loads because they're quality, but economic.  I know some people like 405 grain loads, but those cost almost $3 a round or more.  F*** that.  Other suggestions welcome.

You'd probably be fine with the classic 500 or 405 grain lead.  It's what I would use.  Reload it yourself.  Just beware of 'rainbow' trajectories, so know your holdovers at various ranges.

I have dropped a few elk with my 45/70, but have no experience with any of that ammo.    I always had good luck with the 405 gr SP over a decent charge.  1500 FPS got it done, and was very accurate.

Ya don't need all that speed with a big old bullet,400-405gr @ 1500-1700fps is more than enough,It's an Elk not a T Rex.

Just be aware of your distances and trajectories

Yep.  When I started working up elk loads I ended up trying some book max loads with 420 gr bullets.    1800 FPS out of that little gun,  blew the chronograph over at 15’ with muzzle blast.

I only shot 3 of those, and really needed a better recoil pad.

My elk loads are much more  reduced than that, and drop elk DRT.