The 9x delta is from "a synthetic benchmark that simulates the worst mix of blocking and non-blocking operations". Expect real-world workloads to have significantly less performance impact.
The particular issue is:
"The asynchronous interface requires the O_DIRECT flag to be set on the file descriptor, which means that any access to the file will bypass the cache in memory and increase load on the hard disks. That definitely doesn’t make it optimal for many cases.
To solve this problem in particular, thread pools were introduced in NGINX 1.7.11"
So, NGINX doesn't think it's crazy to deploy on linux. And no, Windows is not a better option. "only the select() connection processing method is currently used, so high performance and scalability should not be expected." http://nginx.org/en/docs/windows.html
...and it was 9x not 8x...