you need a 50cm fin with your 9.4 for downwind racing. For match up racing with your friends you can go with 52cm.
I recommend this two brands www.vectorfins.com
and go with the canefire in carbon molded.
I also recommend www.f4fins.com
and there you go with the D2 in carbon XS.
I will never use that board with a 6.5m sail. Will only use it with 8.m sails and bigger all the way to 9.8m.