I have a Joel Tudor 6 2' Good Karma ( which in my opinion is one of the best single fin short boards money can buy, Heritage in Margate usually has few.) Anyway it came with a 9" fin that I upgraded to a Tudor 9" V Flex. I would also recommend a 8 or 9" Greenough 4A that you can order from True Ames. I have one on my 9 6' Bing and it works great.
I went to Surfer Supplies today on my way home from work . After talking to one of the guys there. I decided to get and 7.0 Bonzer fin. It has a wide base to give me the drive I need. The flex on it is good but not to much to were it is squirly. Since my board has bottom rocker it is made to have alot of drive already which I think will make the fin turn well and be responsive as I want.