Considering your 70 kg weight, you'll gain at best 1 knot of wind at earlier planing if you select going to the FW route for maximizing the lower windrange.
I'm using HS105 + RS7 55 cm fin and Code Red 11.0m2 combo from 7 knots wind up to +12. On par speedwise against a 85-105 kg pal with a FW + 70 cm fin + RSR 10.7m2/Code Red 11.0 m2 sail combo. Defininitely faster than a light weight pal with a RS5 9.0 sail in the lower wind range, no question.
Speedwise and early planing wise (the 2 most important factors to me as well as decent pointing upwind), I've got ± same results with iSonic 133W85 + RS7 55 cm fin and Code Red 11.0 m2 sail combo for my 65 kg weight; so no real need for a dedicated FW board IMHO.
A 12.5 m2 sail is absolutely useless for your objectives (only for XXXL guys going deep downwind on a FW/Apollo), no gain but a lot of pain compared to a lighter, softer and easier to pump 11.0 m2 sail for your light weight. Forget it.
Last edited by Jean-Marc; 13th October 2008 at 12:19 AM.