I dont know, but not sure longer lines help much on the 6 m2.
On the 5 I dont find them needed, as it flies and turns so well (the 6 does too), that I dont really gain power from longer lines I think, it will just give a longer delay probably, and more linedrag.
But I dont know, have only flown the 6 once, still.
On the 8 m2 though, I also by far prefer 27 m lines, no doubt - and use it as my lightwind fun kite in 8-9 knots.
One really fun thing to do with the 5 and 6 and 8, is, in particular if you ride in front of another foiler, fly the kite normally 45 to 60 degree up, and pull the bar in and turn the kite pinwheeling on the spot, let the bar out again and you just ride on straight all the time like nothing has happened - and then do it the other way around shortly after, to rotate lines out.
If the rider behind you have never seen this before, he or she will be amazed !!!
And really fun anyways, just DOING it