In kiting we used the following numbers for carbon tube. Afterall these tubes are not 100 % fibre but a composite of abou 65-75 % fibre and 35-25 % of low modulus resin. Aluminium can of course be used in a pure form of one single material (alloy additions don't really change this) .

Carbon 80 - 125 GPa
Glass 35 - 48 GPa
Alu (alloys) about 70 GPa (never used twose by the way)


From these numbers the two are quite comparable.

Weight of Carbon = 1470 - 1600 kg per cubic meter
Alu = about 2350 - 2700 kg per cubic meter.


This data came from EXEL a big producer of carbon tubes for kites and buggy kites.

I think that we both may be correct here. You stated the specs of pure fibre and I refered to the spec of a layup with resin. It is possible that over the years they were succesful in replacing resin with fibres making the fibre resin ratio alot higher and creating higher stiffness of the layups. I don't know. It has been several years since I was active in kiting.

Wouter