Ive built several 3D aircraft in the past, mostly Cardens and I would recommend building the aircraft as it comes out of the box.Build as close to stock as possible when weight comes into mind. The only thing I do is some lightening holes in light ply with a circle cutter to lighten that up but thats it.

Heres why........Ive flown a lot of IMA and 3D airplanes, and the ones that fly the best are the ones that have the proper area for a particular weight. Manufactuers usually figure out wing loading and design kits around that. If an airplane is too heavy we all know it flys like a brick, but it also does not fly so well if it is too light. The aircraft wont penetrate well if its too light it wont snap crisply and it just doesnt handle as well. For instance I have a 40% Carden Extra 330 that is 38lbs. That is the best weight for that airplane. Ive seen and flown ones that where in the 37lb range and it just didnt fly as well. Just be careful with how much glue you use and watch out on the sanding and have fun..

My two cents
Pete