Hi Extander and PG,
Sorry for my late reply on this topic. I have no good example to compare a starboard iS with an S-type, but I have surfed a Fanatic Stingray 130 TT (68 cm, 136 ltr, freeracer, '03) and a Fanatic Falcon 120 (74 cm, 114 ltr, slalomboard, '05).
In my opninion, I surfed both boards a lot, there are differnces, but if a fast freeracer is tuned well with a good slalomfin and a slalomsail maybe the differences become very small and also you have to mention that normally have a couple of save ltrs of volume and are a little easier to ride.
Falcon 120: gps-display 63.0 km/u, 10 sec run 61.7, 500 mtr 59.0
Sting-ray: gps-display 60.8, 10 sec run 59.0..
Differences are small and since I bought the falcon120 I became more experienced with slalomboards and sails.
In my opinion for recreational use speeddifferences between slalomboards and fast freeracers (at leas in the fanatic case) are very minor, but really become noticably in the upper windrange and whenyou are able to get the max speed out of your slalomboard. Otherwise a fast freeracer is a very nice and save choice. A lot of people simply will go faster with a freeracer like the S-type because it's more easy and fun to use in most of the conditions we meet.
Sorry for the fanatic example, but If I had the opportunity to test a S-type 126 besides an iS111 I think the things mentioned above still are valid