Probably just a bit late, but wanted to add the following...
"Without the barrel gap plus the longer barrel you'll probably get 100 to 200fps increase over a 6"revolver." Actually, most .357 mag loads will go 300-500 FPS faster in the carbine than in a 6" revolver. You can get upwards of 1800-1900 FPS with 158 grainers with the right powder, primer, etc. You an also go with something like Buffalo Bore ammo to get similar performance.
I have a Marlin 1894C myself, and it is a blast to shoot. Very easy to smooth up yourself if your somewhat handy.
Sounds like whichever you choose though, you really can't go wrong. The rifle cartridges have greater range, but the pistol cartridges are cheaper to shoot. Ain't it great to have choices? :mrgreen:
Best of luck with whichever you choose!
Ringo