??
I would be guessing at best at the top video, but have a look at this one:
Scroll to about 1:04 mins and watch Antoine. That was 55-60 knots as confirmed by many sources at the time. Antoine is using 5.0m NP with a proto iSonic 50 speed board. In a solid 30 knots, Antoine would be using 6.7m AT LEAST and I'm sure in flatter waters even 7.2m; So would Bjorn, Micah, Finian, Ben vd Steen even maybe Kevin. That's normal for the top slalom sailors.
There's quite a difference between trying to race at the highest level and going sailing for fun. If I was sailing for fun, I'd always rig about 1m smaller than usual. 30 knots with a 7m is indeed quite possible although (as mentioned in that cyclone video's earlier post) we were using a 6m that day ;)
Ps. What's the red board the guy is using at 0.50 secs on this thread's earlier video? Looks like a gnarly painted Naish hybrid! Now THAT'S impressive to use in +30 knots!!