It looks to me from the last FBL F3C contest in Japan, people are divided basically in 2 groups:
1/. go for 800 class, 2 bladed FBL head with 760mm(Align), 795mm(JR) and 760mm(Quest Impaction),
2/. stay in 700 class with 3 bladed head.
I personally chose the second for my Sylphide.
FBL controllers are either Futaba CGY or JR TAG.
As far as I know, take Ito for example, his Sylphide has a V2 FBL head, 795mm blades(the same blades come with your conversion kit, I suppose), 12cells of 5800mAH capacity to cope with the larger rotor disc, I suppose, but none of them go for 14S.
Hope this give you a good reference.