I am a diehard fan of the 45/70, and Marlins for that matter. They are so much fun to hunt with. If you practice and learn the rainbow game a bit, they are 300 yard rifles. There is a reason that this cartridge has been around as long as it has. It works great on everything. We have quite a few Marlins in the family, and everybody loves theirs. Lightening fast once you get the feel for them. And man oh man, do they pack power, just an absolute hammer. Best penetration around, HUGE wound channels, and knockdown power to spare. Do not hesitate! Go get a new Guide Gun! I have both a ported 18.5 in barrell and a non-ported 22 in. barrell. Get which one you like the best, there is not much difference in accuracy between the barrells. Also, check this page out.
www.garrettcartridges.com