Best thing to do is ride the kites back to back in the same wind. Second best is ride alongside other people at the same time.

Who knows what the exact amount of wind in knots at the kite is required to ride? Who cares, you can't measure it anyway? Riding back to back allows you to definitively compare the two kites.

My experience back to back Infinity V1 vs. 2011 Dyno 18m: Infinity turns much faster, but no contest, the Dyno has way more power and felt more stable in the air with the kite overhead. Relaunch of Infinity seems better, but I didn't test this myself.

Flying alongside others:
LF NRG 16m vs. Dyno 18m, pretty even jumping over 10 knots, but the low end of the Dyno is 1-2 knots lower than the NRG in power and staying in the air.

Turbine vs. Dyno: Very impressed with the Turbine. We were both at the low end of our kites. Seems that the Dyno goes upwind better (as expected), but the absolute low end of staying in the air seems about the same. Relaunch better on the Turbine.

Taboo 17m: Only rode for a short time along the Taboo 17m, but it seemed really good. I wasn't at my absolute low end on the Dyno, but the Taboo rider seemed to have similar power.

Unfortunately I am geographically challenged in this area. Me and my buddy Steve are the only ones demo-ing any kites on Kentucky lake (shocking, I know), and all our kites are old. Maybe I can make it to some kind of demo event this fall somewhere on the East coast or the Gulf (opened to suggestions). That would probably be the smart thing to do before dropping $1500 to $2k on a kite.

So far though, I am very impressed with how happy the Fly owners are with their kites. That says alot.

I'm also considering the fly for my next kite. I currently have the 15M HQ Matrixx which is a great kite, but I'm a little worried about dropping it into the waves, also the QR Takes like 60 seconds to depower the kite significantly in really high winds which is a major problem

For me the kite overlaps fine with my 10...I took out the 10 after I had the Fly out and the wind came up...and definitely overlaps really well with the 12.
I think riding it depowered seems fine, it is a little harder to loop it in strong winds. hehe.

What board are you on? The bigger kites does have more grunt, which is why they are fun in light winds obviously...It might take a little getting used to, but once the wind hit hard, I usually ride with the kite lower, and crank hard on my backfoot. Might be good to take your front hand off the bar and look upwind.
Put more effort on your back foot and the kite will fly forward and your angle upwind will be better.

In what wind does it seem to have too much power? If you move the front bridle attachment forward (does it have those adjustments..I cannot remember), the kite will fly upwind better and have more depower.