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Fly(knit) has a carbon plate like the 4% and Zoom Fly SP is nylon I believe.
There are currently 3 models
Gen 1:
Zoom Fly: A “normal” upper, similar to a pegasus, not flyknit, just a running shoe upper. Lunarlon Foam and Nylon Plate. Many people I know had blister issues in this shoe, but results may vary.
Zoom Fly SP: A softer, nylon shell upper, same lunarlon foam lower and nylon plate.
Gen 2:
Zoom Fly Flyknit : A flyknit upper, a carbon (instead of nylon) plate and react foam that replaces the lunarlon. For all intents and purposes this is the Vaporfly 4%, but with react foam, instead of ZoomX.
Original ZF destroyed my Achilles. Would rub it raw. Also the shoe was very wide and wrinkled getting it laced up.
ZF SP plastic upper not breathable at all. Fits much better and no rubbing on the heel at all for me. This is my training shoe for my VFs
I find the sp also runs a bit smaller.
So I’m struggling to find a shop that even has a Vapourfly 4% let alone one I can try in my size!
For a mere mortal would there be much difference between the Vapourfly 4% and the Zoom Fly Flyknit? Seeing as it’s only the foam that’s different?
Regards
Phil
what are the nike X off and nike off white shoes made off ?
With zero proof… I assume the flyknit are somewhere around 2.5 to 3 percent (compared to 4).
The original lunarlon zoom fly in that strava study showed up about 2 percent faster.
Zoomx is softer and has more energy transfer then react… But react still has more then lunarlon
I also find the fly to be a little more stable then vaporfly
I do call them my vaporfly 3s 
That said, nike.com has the blue vaporfly in Stock in most sizes
https://www.nike.com/t/vaporfly-4-flyknit-running-shoe-v7G3FB
About $50.