Ok, so there's only effect on the power of the kite. And not in the angle in which it pulls me upwind.
But more power means i can push more upwind? Or not?
yes of course more power means you can sail closer to the wind, unless off course you are so overpowered that wind picks you up out of the water and deposits you downwind, then of course you can't go upwind as well.
but anything up to that, more power gives you better upwind performance. upwind performance is not the same as speed tho. bigger kites dont always make you go faster, too big of a kite and you have too much friction in the air to go fast. the same thing for lines, too long lines give you too much friction.