Examples of high performance Rust multi-thread network app w/o async?

I agree. In the local user group, I recommend everyone asking to avoid async and recommend Rouille instead, unless their performance need is extreme. They never had extreme performance need so far, except for a single case (a company whose main product is MITM proxy).

This is safer than you may think, because those who need async tend to know it themselves and don't ask "should I use async" question. In other words, asking itself is a signal that answer is no. MITM proxy case was a rare exception.

I am getting worried recently because some library is async only and people get forced to use async just to use library and get frustrated due to Rust async's high complexity. Things are manageable so far, but I think maintaining healthy non-async Rust ecosystem is essential.