Gearing it will depend on what it is doing now that you like/dont like. it is all a feeling thing really. If it is lacking some grunt off the bottom-mid and that is where you like your power, then add a tooth or 2 to the rear. If it is all about top end speed you want, then either go smaller on the rear or 1 tooth bigger in the front. Just 1 tooth in the front makes a big change. While I have not ridden your Banshee to see what it feels like, most modded quads and bikes I have ridden seem to like a tooth or 2 on the rear the best. The power comes to its meat a bit sooner and easier while the top end power will still be there. You just lose a few MPH, but that is no big deal. Unless you are riding mostly open desert roads and things like that, I would add to the rear. But then again you need to ask yourself this.... Do I need the power to come a bit sooner and harder? If yes, then add to the rear. Or... Does bottom end power mean anything to me???? If no, then take off a tooth or 2 from the rear "OR" and 1 to the front. Tell us about the power delivery and where you ride and lets go from there.
Matt