Every version of AMXX that I have tried increases the pings in my server on the average about 30-40 ms. I have installed and tried .16 which had a huge increase in pings (everyone pinging 150+ instead of 20-30). .20 isn't as bad but it's still noticable, and everybody experiences small lag spikes in fire fights. Almost all my regulars complain about it, so I'm not just imagining it.
The server is rented from Gamedaemons. This is what it gives me through HLSW for the OS v1.1.2.0 (Linux, Dedicated). With the old amxmod I have to use Glib 2.2.