Yes, go with the 45-70, it is a better hunting cartridge.
COTW 8th Edition, shows the factory loading for the 40-60 Marlin as 260 grain bullet at 1385 fps.
Mike Venturino, in his book, " Shooting Lever Guns of the Old West ", show the ballistics of the 40-60 WCF as a 215 grain bullet over 55 grains of 2Fg, for a velocity of 1,480 fps.
Both are a little better than the 44-40, but not by much. The 215 grain bullet from a 44-40 is about 1.150 to 1.379 fps for a 1873 Winchester.
See " My Black Powder Journey ".
https://sites.google.com/view/44winchester/contributors/john-kort/two-peas-in-a-pod-by-john-kort
http://castboolits.gunloads.com/showthread.php?265478-My-44-40-Black-Powder-Journey
A 1881 Marlin in 45-60, which is a short 45-70, and ballistics, from the mentioned book are, a 324 grain bullet at 1,310 to 1,351 fps, may be a consideration.
The 40-60 Marlin and the 40-65 WCF both use the same cartridge case and can be made from 45-70 cases.