After mountain biking for many years, I'm becoming more interested in bike touring and in winter riding. I tour a bit now on my Cannondale Scalpel 3 but would like to add a fat bike to the quiver to open up some sand and snow possibilities. My touring interests lie more in singletrack/dirt road than in gravel/pavement, although I do get that a bit as well. For touring I think I'm looking to ride a 3.5-4.25 tire width most of the time? I'd also like to be able to switch out wheels to a 4.5-5 during the winter to get out and ride in the snow more. So I guess I'm asking for opinions on a bike that has this flexability. I'd like to be able to just switch out wheels depending on my goals. What are everyone's thoughts?