RE: Quickee 500 - best wing tip shape for speed?
The Scat Cat is a really old design, at least 25 years ago, perhaps more than 30. As such, it was developed in the era of K&B .40's of about 1 hp. A Nelson or Jett on it would blow it apart at the first turn, as the wing with the soft 1/16" sheeting just doesn't hack it anymore. If you want to up the power, you need to sheet at least the top of the wing with 3/32 balsa in the 7-8# range, and add some carbon fiber strips to the bottom skin (assuming you are going to do positive g flying at speed). On the wing, you can also add 1/8" to the leading edge to make a slightly sharper entry point without hurting the flying qualities.
The other problem you will have to solve is the balance. A K&B .40 was a very light engine, something on the order of about 12 oz (no muffler way back when). Even a very light .60 is in the low to mid 20's. So you will have to chop off much of the nose of the fuselage, we had to cut off about 1 inch with the later .40's, and mount the servos behind the wing in the tail. With the 60, I would put the tank on the CG, and cut the nose at least 2", perhaps more, depending on the servo weight.