Jetty 9 has a refactored IO layer over Jetty 8 which should garner you improvements in that area. See this blog for information on how and why Jetty is a best of breed in this area.
https://webtide.com/jetty-in-techempower-benchmarks/
Specifically look down for the latency tests where Jetty easily came out on top.
[edit] I should note that this is perhaps not an appropriate question for this forum since it is outside of the intent of stack overflow and more inline with server fault...just fair warning.