huw,
I make 14s7 = to 90kg whch is my weight and I sail a T4.9 cat rigged. (at this stage without the added luxury of a kite)
The T 4.9 Cat Rigged (solo) National Titles was taken out a couple of years back by someone who wieghed 98kg. 15s 10lb
Assuming you still think your too heavy for a light weight boat like an F16 going to the heavier FX1 isn't going to help the situation.