Lots of good discussion here about the airplane design...........

But you are forgetting that for a prop driven model the engine and, in particular, the prop is largley the controling factor for overall speed assuming a fairly clean design of average proportion and low camber airfoil.

Dusteater, if you want to go fast then just get yourself a formula one pylon racer and a Nelson engine. I can't remember what their top speed is but it's way up there. Since you're not actually racing it you can leave off the canopy and arrange for a takeoff dolly and gain yourself another 10 mph or so. That should get you up close to 180 or so.

But having seen a formula one racer fly I think the biggest problem you're going to have is keeping it in sight for very long. The flight path ends up being one long string of reversals in order to keep the model close enough to you to see what it's doing.