Hi

I tried once 2x 27m (54 m) lines on a fiends kite.
Kite was a 16m and wind about 10 knots.

The kite didnt seem to loose response but I think that was becasuse of more wind at 50 m.
The Power stroke is quite long and gets you easily planing in low winds. However the up stroke is another story and it takes time for the kite to get up again and you loose a lot of speed and one need some skill to stay planing and upwind.

Conclusion:
Fun to try and it seemed to work, but a whole lot of lines to rig up and down not really worth it in the long run.

Cheers
Kris

I had a go on a 20 something metre C kite on 64m lines, 2 sets with 10m extensions. Must have been nearly no wind, -8 knots ish, my Speed 17 wouldn't go.
It was like kiting in slow motion, kind of zen, but kind of boring, but worth trying once.
I think there's both more wind up high and a longer stroke.