Blue Skyy,

My understanding of your question is that you have decided on the design of the wing, and are looking to choose the lowest drag wing tip. If this is the case, then the decision is not likely to have a huge effect on the flying characteristics of the plane. A very thin airfoil toward the outboard end of the wing could indeed affect flying characteristics, but only if it represents more of the span than I would consider to be the wingtip. Similarly, to probligo's point, you can't get an elliptical wing by virtue of the wingtip shape. Moreover, the main advantage of an elliptical wing ( actually, an elliptical distribution of lift along the span ), is reduced induced drag, and induced drag, I contend, is not an issue for your high speed plane.

I think you've correctly identified pressure drag as the component of drag to work on. The improvement which is available by working on the wing tip is very limited in any case. Thickness is probably not a big deal. Round those bad boys off to a smooth shape, and feel confident that your wing tip is doing the best it can.

banktoturn