Jan makes a good point. When it comes to most kits and arfs, you are limited by the design and materials to just how light you can make them unless you start making modifications to the structure and use lightweight gear. In other words, pay close attention to how much glue, epoxy and extra wood you add when building a kit. It's very easy to overbuild and end up with something a lot heavier than what the manufacturer advertises. I only scratchbuild and build from plans so I have the advantage of being able to select the weight of the wood and other materials I use. If you go with an arf or build a kit as it comes in the box you are limited to fewer areas where you can shave off ounces.

There is a growing trend today to overpower models. If it call for a .46, people will use a .60; if it calls for a .60 people will install a 1.20 and so on. With a few exceptions, this results in heavier models. Eventually you reach a threshold where the power to weight ratio may appear ok, but the airframe/design and flight qualities start to suffer. An eight pound model with a 1.20 sounds good, but not it that model is a 500 sq in plane designed for a .46.