The key to stabilizing heavier bullets with the MG (1:38") barrels is velocity.
Most MG 22-24" barrels top out at 300-320 grains for cup-and-core or cast bullets, and can't handle bullets heavier (longer) than that.
But if you're satisfied with 300 gr or lighter, an MG barrel will get the job done. You just have to remember to push for the max safe velocity you can obtain.
With 1:20" twist barrels, you can't get much more, anyway. The COAL limitation put in place by action length, and the way that brass bulges when heavy bullets are seated deeply, keeps most shooters from being able to load anything heavier than about 340 gr. The fast twist can stabilize bullets in excess of 500 gr, down to less than 1,400 fps (if I recall my calculations correctly). ...But those loads are only usable in a single-shot. (That's what my 444 Handi-Rifle is for...
)
In my experience, 1:20" twist is actually
too fast for .444 Marlin - especially with heavy cast bullets. ...But all but one of my 444s is a 'Ballard' 1:20" rifle, because I find the limitations of the MG barrel to be worse than the minor issues that come with the steep 1:20" twist.
And the one MG? Well, it's special. It's a hybrid of a Model 36, a 336, an XLR, and a 444. There isn't another one like it, and I figured the MG barrel was more 'fittingly out of place' on a M36 receiver than a 'Ballard' barrel, since the MG rifling didn't come about until the '50s. It was also notably cheaper...