There's only ~0.026" difference in bullet OD and ~4-6 gr difference in case volume between the 45-70 and 444M. A 350-400 gr slug in either will do pretty much the same damage and produce the EXACT same energy at the same velocity.
Way back in the distant past I read an article about the 444 and the author implied that the 444M wasn't much good with bullets over 265 gr and the velocity was too low...so I didn't bother with the 444M until recently.
In the interim I went from Hi-Velo small cal light bullet to larger cal, heavy for cal bullets, realized what has been evident for a very long time and finally woke up to what I had been missing out on...for close in work you can't beat a BIG bullet at relatively low velocities and the 444M doesn't have to shine NO STINK'N' 45-70 SHOES.

;D :
I never liked that big 45-70 rim in anything except a single shot so when I was looking around for something to build on a SMLE receiver I picked the 458 American...I could have just as easily picked the 450 M or the 444M but by picking the 444 them I would have missed out on doing this 356W/444M/??? swap barrel Marlin 336. Things seem to work out in the end when you don't get locked down to tight.
I have big bore rifles from 375 to 50 cal including 45-70 to 45-120...and there were BP cartridges in 44 cal just as long or longer than in 45 cal....the 44-100 Wesson has the same case volume size as the 45-120.
It's just circumstance that brought the 45-70 into deeper consciousness and made it the favorite toy-boy and nostalgia took over from there.
You can shoot the same weight bullets in both cases, loaded to the same COAL, at the same pressure, to the same velocity...it's basically the same arguement between the 45-70 and the 450M...a tempest in a teacup and much ado about nothing. ;D
Be happy we have choice!!!!and enjoy your 444M...or WHATEVER caliber you chose. 8)
LUCK