Hi Marin I have ben sailing on the Vapors (9.3 and 7.6) and the GTXs (8.0 and 7.0) this year and have enjoyed them a lot. The inset clew on the Vapors make them feel 'small' on the water, (well as small as a 9.3 could feel!), and they feel like they are easier to handle as a result. As you would expect, they feel blisteringly fast when you are wound up! They do have a very good top end, at your weight on a 110 slalom board I would think about the 8.4.
Would echo Vandos comments that the Vapor feels more stable than the GTX, and the Vapors certainly have a wider wind range, they seem more able to deal with minimal downhaul/outhaul when its light, but twist off really smoothly when fully downhauled.
Goes without saying, but try to get the Gaastra masts as well, they add a little extra zing to the sail.