A 44cm fin is pretty big for a 5m sail , i would have changed the fin to a 32-34 and left the 6.6 up, maybe a bit more outhaul would have helped?
I use a 34cm choco fireblade on my 105lt board with a 7.5 mt sail in 18-20kts no worries ,
if you are over powered change to a smaller fin first
Why you might ask?
with a smaller fin the board sits lower in the water and is much easyer to handle.