I just tried the 8 on the 21 meter lines today and loooooved it!
I had ridden it a bunch with the extensions but decided to give shorter a go as it was gusting to 40 knots today. There is little less power with the shorter lines but not much, I did find the kite easier to fly on the shorter lines than I expected. It seems like it is easier to tell what the kite is doing with the extensions off - which is good as this is one fast kite!
I wanted to try some loops with the shorter lines but didn’t have the balls for it today. It loops great with the extensions though. Definitely try both the shorter and longer set up to see what you prefer.