Blue Skyy,

I think that the best tip treatment, especially since high speed is your goal, is a smoothly rounded tip. The main benefit that you could hope to get from any unconventional shape is lower induced drag, and induced drag is negligible for high speed level flight. As you point out, pressure drag is the culprit, and a smoothly rounded shape is where it's at. Regarding thickness, I am guessing that, within the range of thicknesses that you can practically attain, thickness would not be a big factor. The classic reason not to go too thin is that weight will likely increase if you try to make a thin wing strong enough. This is bad, because induced drag is proportional to the lift coefficient, and the lift coefficient increases in proportion to the weight ( for level flight ). For a plane with mandated minimum weight (like a pylon plane), this might not matter. For a plane with unregulated weight, you want to be as light as possible, and an overly thin wing makes that tough.

banktoturn