I am also rebuilding an Avonds Eagle for (twin) turbine. Threw out the 6mm ones, replaced with 8mm. I even considered going to 9 or 10mm...
From an engineering calculation point of view the 6mm will be plenty, but be sure never ever to nick, hit or dent the stabi hardpoint....else it is likely to fail.
So common sense sais: go safe, go 8mm.

Rgds
Hank