ASIO does all that. And it compiles to machine code. What you're basically trying to argue is a well-written C++ application will be slower than a well-written java application. That's not going to happen -- at best they will be the same performance.
Netty certainly has a more impressive list of projects using it in real-world high-volume scenarios. That's probably what wins in this case...enough high volume end users such that you've gotten enough edge cases to tweak the software and iron out bugs.
If I had to pick something in the C/C++ space to implement a custom proxy, I would probably stick to something where I could find a similar list of established high volume real world users. Facebook's Proxygen, or some customized HAProxy maybe.
I was trying to say in a nice way that it's unlikely you've created something as fast as netty because a lot of people spent a lot of time optimizing it.
Netty is also a lot easier to extend and more portable
