G'day Matthew, Just in case you're still looking at fins, the Sonntags work beautifully with Isonics and well worth the outlay. I won the masters division in the Lancelin Ocean Classic downwind marathon this year on a 2014 Isonic 107 with a 38cm Sonntag SL-R and 7.0 Reflex. Despite being really underpowered in places the fin kept gripping to trim the board nicely and stay in front of guys on bigger gear. Control in the chop, and top end speed are outstanding characteristics of these fins too, so it terms of top performance over a range of conditions the Sonntags are hard to beat.
Cheers, Shane O'Neill
Last edited by shaneo; 14th May 2014 at 09:41 AM.