salmonbug & strykaas,

I'll assume you are both flying the same plane. Looking at the picture the salmonbug posted, I would say there are few things you could do to get some drag reduction. No wingtip treatment for induced drag reduction would be among them. You are optimizing your plane for high speed flight. At high speed, the CL will be small, and induced drag will be correspondingly small. There are several things you could do to reduce profile drag:

1) Put a nice fairing behind the engine, leaving a gap or channel for cooling flow.
2) Put nice rounded wing tips on the wings. Some people will tell you that a square tip, as is on the plane now, will reduce induced drag. I don't believe that, but I know that a rounded tip will reduce profile drag, which probably matters much more for your race.
3) Make some nice smooth fillets for the inside corners where the vertical stabilizers meet the fuselage. Some soft balsa stock could be glued there and carved/sanded to nice, smooth, rounded fillets.
4) Add some fillets where the wing joins the fuselage.

banktoturn