Any well built wood framed sailplane will outperform the foamies.
I'd start with Bird of time. Build is a little challenging in a couple of places but not hard if you pay attention to detail.
Use yellow wood glue (Alphatic resin... Titebone II, Elmer's Carpenter's Glue) for most of the build and use just the right amount for maximum strength with minimum weight.
You can convert just about any wood structure sailplane for motor-glider. Its possible to come out the same weight as a motor glider than as a pure sailplane because of the lead ballast typically needed for the sailplane. Then with modern digital mini or micro servos replacing the old heavy low power analogs the kits expect you can save even more weight (and often need ballast to make it fly right in windy conditions...)