I went out today here in 18 gusting to 25. I was using a 6.6 which was overpowered (for me) I changed down to my old 5m wave sail. I ride a Xcite ride 130lt which has the standard 44cm fin.
This fin seems fine on the larger sails but I recall something about dropping down the fin size if you go to smaller sails.
Can someone offer some advice as to if this is correct? I know that a 130lt and a 5m sail seems an odd combo but until I can get a smaller board for heavy days it'll have to do, so I want to make the most of it.
Ellobuddha, yes you can come down in size as you come down in sail size. If you have the black material JP fin, look at a G10 style if you can get a good used one from the outlets, will work better for you. I was lucky enough to pick up a 2nd hand JP Supersport 46 and its a lot more fun and far easier to handle. 
Outlet recommended I be on lookout for a 40cm and a 36cm to fill in the gaps on the 130lt. Have already, a 32cm that came with a X-Cite 110.
Hope this helps.
Mineral
Thanks Mineral,
I bought an old Mistral screamer and he threw in 4 fins ranging from about 42cm (g10 i think) down to about 36cm slalom fin. Ill have to check them out more closely as we're now getting some real wind here. Time for some experimenting.
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.
