Well, the background to my campaign is basically that your race is just moving out past your own system, so you get to explore and colonise a bit before likely running into the other players.
As regards movement, well, your army isn't likely to do much just sitting there, and scouting cavalry (or fliers) are going to move a lot faster than heavy infantry on foot.
I suppose it might be possible to convert the basic frame work over to a fantasy setup, but it would pretty much mean rebuilding it from the ground up, considering the stuff you can research, build or customise is all sci fi.
If you want to go fantasy, that Exalted one probably isn't a bad place to start. I can take a look around, I may have other stuff lurking on my hard drive that is suitable, or adaptable.