In fact, its 1.4.18, not 1.4.22. The Ubuntu repo is not uptodate. Consider compiling haproxy from source, to have the latest bugfixes in it.
Anyway, the build has tcp splicing enabled, so with the
configuration changes I proposed, you should be able
to handle the load.
Remember to check your kernel and conntrack settings,
they may also slow down your machine.
