this is not a dis on this kite. people confuse tight turning with speed. these kites arent fast, and can be set to a heavy bar pressure, but they can still be turned super tight and with extremely consistent pull and performance. heavy bar pressure and slower flying speed help hold that back for easy straight line tracking and predictable feel.
this is what you want.
otherwise your looking at a slingshot t3 7m or older crossbow 7 or convert (t3 and xbow are very strong for their size, heavy steering resistance/pressure. convert just plain slow) maybe a SS key but i dont have experience with that one in small sizes, looks like same shape as t3 tho.
It's not an 8m, but I have been really happy with my Ocean Rodeo Prodigy 7m on the criteria given by the original poster -- it is really stable deep in the window in gusty conditions, has lots of depower, and is very relaxing -- doesn't dart around unpredictably like other small kites I've had. If you crank the bar it turns pretty well and predictably, but it doesn't respond a lot to small bar movements. I have found it to be much more fun and confidence inspiring in the 30mph+ range than the other small kites I've had. YMMV.