I can't speak for the 444 Marlin, but my 15 inch plus brake 376 Styer is accurate and effective at 300 yards when I do my part.
As far as effective goes, it has alot to do with what bullet you are shooting.
The Barnes X and Nosler Accubonds are effective and efficient down to about 1650 fps from what I have found out.
So as long as you are shooting at a range you have practiced at, and are using a bullet that will open at the velocity you are putting it at, then it should be effective.
Kevin