howie--The 45-70 is the Real Deal on things that bite. I would not shoot the factory 300 grain HP at hogs. It is poison on deer, but doesn't penetrate like the 405 grain factory stuff. I used to shoot a lot of jacketed bullets, and found that they would come apart and fragment when you hit something hard. Good cast bullets give much better weight retention, and will usually mushroom to nearly twice the caliber. The bullets I have recovered have been shot into a clay bank. I have never recovered a 405 grain or heavier bullet from a hog or deer. They always exit, regardless of the angle. I have never shot the 350 grain stuff, so I can't pass judgment on that.
If you are getting a Marlin and want to reload, a 400 grain Speer over 50 grains of 3031 will give about 1850 fps, and will nearly cut down a 6 inch diameter bull pine with one shot. It kicks in that rifle too, but is an accurate load.
I will be shooting a 30-1 lead/tin bullet at 1225 to 1250 fps whether I shoot a 45 or a 50. The 45 will weigh 530 grains, and the 50 will weigh 624. After you see the ammo, you tell me which one you want me to shoot. Shoot straight, rdnck.