I got an 07 SX Medium to have just 1 slalom board and one that would last me a while so construction was important. Build wise a big improvement in strength over the earlier F2's with mine still not having a single ding but it does come at the expense of a bit more weight over say the fanatic falcon.
They are fast, i'm yet to see anywhere near the limit on these I know of one sailor here that has done 37 knot peak on one. The tail for being quite wide feels very free through the water, they also prefer a bit smaller fins. They are a bit fin critical, i've found that the right fins make them ride at best trim. The fins to get the most out of them seem to be the standard f2/meanline & I think choco shapes though I haven't tried the usual fast fins such as tectonics or C3.
For 105 litres it feels pretty big due to it being put into a relatively compact shape. Although shorter the wide nose helps you drive through the chop as it refuses to bury. Double concave in mid section and rounded rails make the ride pretty good, due to this the SX's don't plane quite as early as other boards but remain controllable for longer. Some people claim spinout with them but i think it is more that with such large cutouts you shouldn't load the fin until moving.
I do love this board, it is a technical board if you want to get the most from it but it does reward. Did I mention the gybing... i'm not such a good gyber but this is the best slalom board i've ever been around a corner on. It's sweet spot sail wise is 6.5-7m I wouldn't put anything larger than a 7.8 on them fins 32-42 (if you get the 36cm fin keep it

). Try the mast track from middle-back.
Graceman what are you doing stepping between the back straps?