Play to your offensive strengths vs. their defensive weaknesses, and take away their strengths. If it makes sense within the game plan, spring a surprise on the opponent. Don't run a -5/double team leading scorer because you think it will work. Do it if it makes sense i.e. your opponent doesn't shoot many 3s.

If you are referring to tonight's game, I'm not sure a -5 is a good call (maybe -2). Your opponent doesn't shoot a ton of 3s, but he has a lot of perimeter players with speed and decent PER.

Best way to spring an upset is to have the best possible game plan.

Normally you play slow down when facing a much better team.  The team you are playing has a weakness, though.  Try to exploit it.  They are very strong defensively with their big men, but their guard defense (and small forward) are average defenders.  Go after them.  You have a guy on the bench that can hit outside shots (well, he hasn't been all that efficient yet) perhaps he can put you over the top.  Good luck