Well, all new devices are running 5.x for one thing, and almost everything that's currently on the market (and going back a version or two) can run 5.x, so there's little reason for it - I mean, it's the likes of the iPhone 3GS that might not be able to do so, and even that I'm not sure about, maybe it can. Certainly the 2010 (first gen) iPad can do so, as can the iPhone 4, and there's been at least one iteration on both of those since.
I don't know what you'll save or lose if you reset, but you could always back it up first?