I've tested few QoS options with quake 3 servers.
Intel PRO/1000 MT Server Adapter seems to be the best choice.
Here's picture of this NIC (if you want bigger resolution click on it):

This NIC (Network Interface Card) supports both Layer2 and Layer3 hardware tagging:

You can select special QoS filters for this adapter (weed server for example):

*This will tag Quake3 packets to take priority over networks and lower your ping.
Number 5 is marked as critical/Video priority.
You should also ask your ISP what's the Maximum Transmition Unit (MTU) they support.
Your ISP should support MTU to at least 1504 because for QoS you'll need at least 1504 bytes of MTU.
here are the results (click for larger picture):

fish.meh is my brother ( !333!NonE )
and you find me under nickname !333!SpC

we're on the same internet line yet we have so much difference in pings this is due because my brother uses normal ethernet packets and
i am using QoS tagged packets everything else in quake 3 is exactly the same .. ( maxpackets, snaps ... )
Difference was and still is approx 20ms whole time of playing.
Intel PRO/1000 MT Server Adapter costs approximately 133 €uros so if you want to lower your ping you should consider buying it.
QoS only works if your ISP and devices (routers, switches etc...) supports MTU equal to or larger than 1504bytes.
Kiedyś cfoss probowalem ale to nic nie dawało.



