I don't use 30-40 Krag, but it should be good for 200yds with a 180gr SP. Ballistically, it's very close to the 300 Savage and both are adequate within their respective range. Energy runs over 1000ftlb at 300yds, which is more than enough.
Remington's ballistic table give the 30-40 180gr Core-lokt load the edge over the 300 Savage 180gr Core-lokt load.
Reloading tables give the 300 the edge by a smidgen.
NCsmitty