Splitting hairs I guess, but once you go down this path, it makes sense to finish it. Per the graph at the beginning of this thread, we are talking about rear attachment points X and Z. What you say would be very relevant if you are using stopper knots, or some other device that limits bar travel on your chicken loop. For example, if you have a fixed 3 inches of throw, you would get more depower and more range on X. If on the other hand, your bar is set up so that you have a little excess throw (you can sheet in enough to slack the front lines and sheet out enough to slack the back lines on either X or Z) then you can depower the kite just as much on Z as on X, PROVIDED that you move the bar farther when on Z. So it is not correct to say that setting X has more depower than setting Z unless you are willing to limit the amount of throw (most people don't), which has to do with personal prefference on how you set your bar up. The way the Slingshot bars come from the factory, there is quite a lot of excess range when you combine the chicken loop throw with the trim rope adjustment. In other words, the Z setting will depower just as much as X provided you push the bar a little farther away from you. And we're not talking a lot of extra movement here.
The same concept applies with turning speed also. For a given bar movement, you will turn faster on X. However, if you move the bar a little farther on Z, then it will turn just as fast. And since these kites turn so well, you almost never need to really crank the bar all the way (however, if you are comparing turning speed with the bar cranked all the way, then X will turn faster). It just boils down to personal preferrence: Do you want the kite to be more sensitive to smaller bar inputs along with heaver bar pressure (X) or vise versa (Z).
Again, correct me if I am wrong.