Toomey T5s or T6s on a Banshee. I saw a dyno somewhere of pipe comparisons for a Banshee and the Toomeys were on top.
FMF Pipes do good things for the low/mid but taper off torward the top, and FMFs are cheap(ish) for a Banshee too.
Your +4 crank will already give you torque lower than a stock one, and if you size your carb properly, that will also augment your powerband where you want it depending on carb size and jetting, so you have options.
Hope this helps.