I'd guess your figures with the LE are probably correct. I too shoot the .405 Remington and it does not shoot as flat. However, as thejanitor has stated, ya gotta shoot it and learn it. A mil-dot scope helps a lot, but for some unknown reason, I don't use one. I shoot the .45-70 much as a traditional long bow shooter does. I just have a "feel" for it. It's difficult to explain. First you have to find a load that's accurate in your rifle and comfortable to shoot and then bang away with it at all different yardages and learn what it does. This Spring, I intend to slow down my load from the 1950 fps. I'm using to make it more comfortable to shoot. Then, I'll have to learn it all over again. When you learn it, you can take a deer, coyote or woodchuck at 300 without a problem.
Pete