A word about the weight of balsa versus carbon fiber. I did a lot of careful selection of wood and carbon fiber. What I concluded is that balsa is stiffer for the same weight or even lighter, hands down. I probably saved at least 10 grams (about 20 percent of the model weight) by using balsa. The trade off, however is a relatively fragile airframe as compared to carbon, The carbon rods also have less drag aerodynamically. We are not sure this is a real disadvantage though as the extra drag from the truss structures help give the airframe a more consistent and slower speed.
For this model build, I used mostly balsa, some boron (elevator balsa pushrod is reinforced with 4 pieces of boron, fuselage side stringers use boron on the inside and outside). and some carbon fiber. Scott Brownewell had suggested some really thin carbon fiber strips for strategic locations. I split this in halves or thirds and used very small strips on one side of balsa key truss structure pieces that I noticed had a tendency to break (e.g., from my first real F3P practice session two Friday nights ago). I also used carbon rods rather than balsa on the upper sections of the airframe- places where you tend to bump into and snap balsa stringers. The results turned out great. The airframe is very strong and weight is reasonable at about 47 grams ready to fly.