Using common sense about a two stroke engine, more back pressure equals more torque and less back pressure more top end rpms. This is why a longer exhaust manifold will make more low end torque than a short, because it takes more force to push the gasses out of the exhaust. In turn you can apply this to the exhaust stinger. A larger diameter stinger will flow easier than a smaller diameter one so the larger will have more top end and the smaller will have more torque. Personally, I haven't experimented much with the stinger so, I can recommend one, and there are alot of factors thapt effect the ideal combination (engine, gearing, fuel, carb tuning, race course layout, driving style, etc.), so you'll have to try them out. I hope this helps and I gave you the right insight to help you make a decision.

Keith