I have discovered something today and wanted to share the information. I decided to install the original client of QuakeWorld (v2.30) and connect to a modern server. I succeeded, but noticed that the frame rate was also limited to 31 fps (checked using FRAPS), just like in HexenWorld, as described above. Connecting to the server with a modern QW client (ezQuake) didn't come with this limitation which showed me that the issue wasn't server-side, but client-side. I did a bit of searching and found...
When I run Hexen II, I get 72 frames per second (as expected). However, today I set up a HexenWorld server on a remote Linux machine, connected to it with the client and noticed that the frame rate is limited to 31 frames per second. This happens regardless of the HexenWorld client used (hwcl.exe or glhwcl.exe). Could anyone please advise me what to do to remove this limitation? Is it possible, or is it something hardcoded? I assume that the frame rate may possibly be limited by some server setting...