Hi Davide and Screamer,
I can frankly say that I tend to think much like Davide here, because I think about my biggest board (with a larger fin too) to get me up and going in the very lightest of winds, and if things come up I'm on something quite a bit smaller. Admittedly, I'm surmising that Screamer wants to be powered up on the iS122 and the 9.0 to take advantage of the other side of the spectrum. Many believe that slalom boards are designed to be driven hard and focus accordingly. Believe me, there's a lot of truth to that philosophy, but I also think slalom boards are particularly potent and effective on the light side of things too, as evidented by Davide's successful switch from the RogueWave to Sonic.
As a aside about the ML, it's my experience that they don't disintegrate that easily, despite their notable light weight. My 1998 9'4" ML Course Slalom is still quite sound and going strong. However, I have to admit that its design is a bit outdated on the scheme of things, but I'm still quite fond of it.