In fact, it is my firm believe that this board does not go much faster. I used to own one, and it had a definite top speed that you really couldn't press further.
Not true. Roger van Tongeren (±100 kg; nicknamed "podjur48") did almost 40 knots (72.7 km/h) as a Vmax with HS111, a RS4 6.2 m2 and a very small fin (26 cm if I recall correctly) back in 2004 during a pretty windy day at the Horst Strand speed strip in the Netherlands. A video and his GPS tracks were freely available for review to anyone at that time (http://forum.windsurfing.nl/viewtopic.php?t=6472).
He next did ±42 knots on Sonic 100 (75.7 km/h) and ± 40 knots on Sonic 90 (72.9 km/h), so HS is certainly not a slug to somebody who truly has the skills (and balls) to go fast...Oh, BTW, Roger is the timekeeper on gps-speedsurfing.com.
Still plenty of room to press further as you said...