But I like the quality of the older Marlins better
That, I cannot argue. I've seen too much not-so-good out of the Remington stuff that it will be awhile before they regain my confidence, but I understand that quality is improving.
In getting your heavier bullet to stabilize, you've probably had to resort to near-top speeds, which is something a tighter twist would not demand, you could slow the bullet down if you wanted.
My own .444 was an SS model, and I found the range of bullets I could fire to be like yours, I just had to zing 'em on out there fast, or groups would start to open up, finally keyholing. That area could be construed as "Marginal". Not that it kept me from using the rifle, it's just I felt some versatility was lost.
I finally settled on the 265 Hornady.
The 355 grain Beartooth bullet is similar in SD to the .458 Piledriver Jr, and would be an excellent choice for big animals/bone-breaking. I use the PD jr quite a bit.
But you pretty much stated your case with the vintage of rifle you like, and it simply was not available with the tighter twist.
