Just thought I'd add my two pence worth to the debate. Having sailed a Stealth for two seasons on tradition rudders I've recently purchased the new Stealth F16 with T-Foils. It was noticable from earlier light wind outings that the boat is very stable for/aft particularly downwind. A very planted feel with no noticable side affects.
However last weekend saw some decent wind and the chance to see what they could really do. Twin trapeezing everywhere, try as we might we just could get the boat to stuff the bow in. On one occassion when lossing my footing downwind and swinging forward into my crew I was sure it was cartwheel time and would have been on my old boat but nothing more than a slight bury with no water over the top of the hull.
There is another Stealth F16 at my club who has been racing with the standard rudders while waiting for his new T-Foils. There is no difference in performance between the two setups. Until it gets scary downhill that is!

John Pierce took a load of photo's and some video of the weekend so will post when we get organised.

Wouter - If you're there, I've very regretably had to pull out of Texel. Maybe see you next year.