When playing netpanzer with a big map (like the OpenWar map), and 6-10
players, the game slows down to such a crawl that it's no longer
playable at all. Units move one square every few minutes, and sometimes
they don't react to commands for several minutes or they stop responding
altogether.

This is usually accompanied by very high CPU load in both client and
server, and messages like the following in the server:

    Network send error when sending to client 52: message sent to
    unknown client.

I haven't looked at the code, but it seems to me that this state is a
combination of an algorithm that doesn't scale well, and network code
that doesn't cope with broken or timed-out connections.

Some specs:

Server
 - 466 MHz Celeron II
 - 386752 kB RAM (~16 MB free while playing)
 - 512 kbps internet connection (never saturated during play)

 Client
 - 1,2 GHz Pentium M
 - 1024 MB RAM (~70 MB free while playing)
 - 10/1 Mbps internet connection (never saturated during play)

Obviously, I have no idea what kind of specs the other players have.

If more detailed information is needed, please let me know!