In case it's not too late, here are some numbers. Carbon fiber is something like 20-30x stronger than spruce or basswood for an equal size, but it's also heavier. If you use solid 1/8x3/8 carbon caps, I'd bet everything else
in the wing will break before those caps. Some quick math shows each 48" cap would weigh about 2 ounces, while a wood cap of the same size would be more like 0.6~0.7 ounce.
If this page
is still authoritative, you just might squeak by with a solid carbon spar, depending on the CD.