If the ioquake3 server and ioquake3 client are from built from ioq3 git master or downloaded from test builds page, the client uses a slightly different protocol – though I wouldn’t think it could increase ping. Run the client from command prompt using ioquake3.x86_64.exe +set com_protocol 68 to use the original protocol.
I’m not familiar with high ping to LAN server issue. You could check the Gog Q3 and ioquake3 client config to see if they have different settings for rate, snaps, cl_maxpackets, com_maxfps, and r_swapInterval.
Good settings are probably
- rate 25000 (In menu as Setup -> System -> Network -> Date rate “LAN/Cable/xDSL”)
- snaps 20 (default 20, should be the same value of server’s sv_fps)
- cl_maxpackets 125 (default 30, input packets sent to server per-frame, cannot exceed com_maxfps)
- com_maxfps 125 (default 85, frames per-second to render)
- r_swapInterval 0 (no V-Sync)