Lucky,
Welcome!
As for the BC, nice start there. It will safely handle the Marlin loads, this directly for NEF and many of our board have pushed to that level and some beyond. Should you desire to go beyond you are on your own and more man than most of us. Your shoulder will usually tell you to stop before the gun will. That metal buttplate sends a real loud and quick message when you push a 400gr or more in the 1700-2000fps range.
I pushed some out the barrel VERY close to 2000 (400gr Speer) and I'll tell ya it ain't fun. Never got to hunt with mine, but those that have ALL say it's not necessary either.
I will ad that I once read an article on calibers for elk hunting. this guy covered everything from 270 Win to 375 H&H, and the 45-70. He gave accounts that matched everything I've read about all the other calibers. When he mentioned the 45-70, he basically said, that when you see and elk shot with a 45-70 using a 400gr bullet at 2000fps, you have to see it to believe it. He called it devastating. I have no reason to doubt him, based on the amount of recoil it produces.
Welcome, again, and enjoy that BC.
This was mine.