I use the iSonic speed W53 mainly with 6.6 & 7.7 m2 sails and I agree with Mark it's a perfect board to speed in open water all the time, providing the chop stays in the small to moderate size. In heavy chop, a dedicated high-wind slalom à la iSonic 80 would fit better IMHO.
Cheers !
JM
PS: check these old threads about iSonic speed W53:
http://www.star-board.com/forum/showthread.php?t=8998
http://www.star-board.com/forum/showthread.php?t=7527
http://www.star-board.com/forum/showthread.php?t=4324