That would work too, but I like the opposed roll as it forces the players to make a decision on how many dice to allocate to special and how many to movement. If you did the 1-3s only how would you allow for a failure of the sneak? More 6s than 1s maybe? or would you just assume there was no failure?
Against mere minions I would assume no failure, sometimes it is about the story.
But the more 6's than 1's would work well I reckon.
I will almost certainly use the method I did though, as it works better when faced with proper bad buys with 10 dice or whatever.