Sean, raise the extension amount and leave a gap between the extension and the pulley - this is how Martyn Ogier sails his as he is a man mountain!
They are not only a flat water speed sail, they work really well in chop and were designed for open sea slalom in maui! Obviously they do work well on flat water.
I have had the same experience as you with my 8m, I went into a gybe at about 30 knots and the foot ended up under both my feet meaning I couldnt get them out of the straps.....I am now a couple of cm taller after the resulting wipeout. Since I have raised the extension 2cm and that has cured it. Rest assured the new sails have a slightly higher foot to stop this. People on Starboard dont tend to have the problem and Tom designs them with his Isonic, I found the foot catches the rear strap a lot with my 7.3 and my RS2, other sizes I dont have a problem with.
Another tip as Waiting4wind said is to move the track right back, I have experimented a lot with track positions in boards from 78cm-69cm-59cm-54cm with different sizes of sail, they all perform slightly better with the track right back. The noticable thing is with my 7.3 and 59cm RS2, if I have it forward as I bear off I sometimes get pulled over the front as I exit a gust (at random it seems), with it back I dont.
The 6m I agree needs 2cm less downhaul than printed, all above that are fine with the printed settings. Although I tend to still be in the habit of looking for a loose leech which these sails do not need as much, the twist is designed into the shape of the leech so you can run it without it being baggy. The clue is in the tension of the luff tube as you pull the downhaul on. Its worth trying them with a tighter leech in choppier conditions, I get faster speeds in chop with less downhaul, but still get fastest on flat water with max downhaul overpowered. If I wasnt so lazy I would swap between 2 consecutive sizes, big with loose, smaller with tight and see what my max speeds are.
I have done an article on the new GPS's, not yet sailed one myself but Martyn did well at Weymouth speed week on his.
www.redsurfbus.com/2012/10/new-kit-to-be-tested-for-2013.html