Re: 45-70 Gov. VS .338 MAG VS .300 Mag.
The OP, bigrick37, stated he wanted another rifle. I am happy to help someone buy another gun! Having started my centerfire shooting with a Rem 742 in 30/06 I am a huge fan. Yeah, it will do it all just fine. But bigrick wants another rifle.
300WinMag is today's 30/06, a do-it-all. But he has an '06 and another 308cal makes no sense in a two gun battery.
45/70 is powerful up close - with handloads. Bigrick didn't mention reloading and there is good factory stuff but the 45/70 needs the custom touch of handloading to develop it's superior knockdown punch. But still possible.
338WinMag is an awesome big game cartridge. Tons of energy, long range, big well constructed bullets, everything you could ask in a heavy hitter. It's biggest advantage is superior Factory Loaded ammo. Full range of Barnes' finest in their own Vor-Tex line, and Nosler puts out a top quality in house line of ammo with their best bullets.
In my mind it is the caliber to extend bigrick's hunting selection and be able to get maximum bang for his buck.
But it is still an opinion.....