Steve Arndt's Posting Carbon rods in CD spar and fabric in carbon D-cell
http://www.sailplanehomebuilders.com/arndt_news_posting.htm

GRAPHLITE CARBON ROD by Jim Marske 
http://www.sailplanehomebuilders.com/projectofmonth.htmComposite Spar Sizing:  http://webpages.netlink.co.nz/~rajiv/ras-archive/apr96/0281.html(Note: Newsletter removed from this link ... Posting was not archived.  As I recall, this posting
Indicated that 72,000 would be a concervative value for Carbon Tows.  I have seen 49,000 also.
In contrast to this posting, Irv Culver used 90,000 psi for Carbon Tows) 
Bottom line, use the new carbon rods as above!