I had a Leupold M8 4x33 on a Marlin 1895, and it worked very well. One of the things I particularly liked about it in that application was that it has a comparatively small eyepiece diameter, so I could mount it good and low while still having access to the hammer underneath it. Very light too. IIRC the FXII is of similar dimensions.
I have also used one of these scopes on a 9.3x74R double rifle, and a couple of other 4x scopes on other rifles. A Meopta Artemis 4x32 in particular is one I am very happy with - such a pity they appear no longer to make them. For big game at distances from close in to well past 100 yards I think they work very well. I've shot a good number of pigs, some buffalo and various other game, standing and at full gallop too, using these scopes at these sorts of distances. Fixed scopes also have fewer lenses than variables, so can be lighter and, in theory at least, pass more light (all else being equal).
A 1.5 - 6 would also be a good option, or perhaps a 2-7 - I have a couple of each of these - though you might find it hard to get one with quite as small an eyepiece diameter as the Leupold 4x.
