RE: S-Type 93 or 104?
I'm 83 kgs and generally prefer the ST-93 over the 104 in the windspeeds that you mentioned. The 93 will carry a 6.5 almost as well as the 104, plus it is smoother and gybes better than the 104 for me. I also find it to have a crisper ride and more of a slalom feel than the 104. Overall, I think it is a great board for blasting around whether it is offshore on big swells or on choppy water near shore. I also have a ST-115 and I even prefer that to the 104 in most conditions.
Hope this helps.