The stock V6 rear end is a 7.5" ring gear. fine for econo cars, but not high performance. the V8 cars use an 8.8" ring gear which is stronger.
Gear ratio selection will depend on a few factors. is this a track car? or mostly street driven? what type of supercharger is on it? a centri blower will need a different gear than a roots/twin screw.
the higher (numerically) the ratio, the quicker the acceleration. it will also limit your top speed. this will also create a traction problem. lower (numerically) will offer better economy for highway cruising.
i dont know what ratio the V6 cars got from the factory, but i would assume 3.31s. upgrading to 3.55s would not be worth the cost, IMO. even 3.73s would be a toss up, when weighing the cost/benefit. now, if you had 3.55s stock, then i would leave them as is with the supercharger.
the easiest way to tell what the ratio is to look on the rear differential cover. there is a white sticker that tells you the ratio.