I have run two Marathons with the Flyknit Racer and one with the VF 4%.
Logged about 500 km with the Flyknit Racer before retiring them, and about 150 km with the VF 4%.
The Flyknit Racer has been for a while my favourite racing shoes. They definitely feel more stable and even lighter than the VF 4%. They will also last much longer.
My first experience with the VF was mixed; I found it weird to wear first time. My steps were feeling too soft and the shoe looked really unstable.
However I have decided to use them anyway in a Marathon that I have recently run. And I don't regret it. For me - not sure exactly how much you could attribute to placebo - but i really felt the shoes helping me to push after 35 km or so.
I ran 2h31 with the Flyknit and 2h30 with the VF. I believe I was at a very similar shape in these two races.
Overall, even though they are both racing shoes, they feel very different, but it can be quite hard to explain how different without wearing them.