I found that as long as we where twinning there was a big improvement with the T foil. It seems to make it plane high enough to keep the 2nd chine out of the water. If you sail it really flat with your weight as far back as you can and the T foil on enough so the bow is about an 2cm out of the water it is really fast, if it is not in this trim it is much slower. The T foil also helped maintain speed though the tacks.