Tried this last night and it made a mjaor increase in performance in latency terms.
All information from WoW Euro/American Tech forums.
1. If you have not done so(Europe Clients) Download the " Official Registry change to disable patching while playing" from official Tech forums from WoW Euro ( www.wow-europe.com ) I cannot login WoW Euro at moment will update once i got link. American Clients can do the same(from USA site!) or they should have an option already to disable this.
Both Euro and USA gain a massive improvement with following
2. Open your My Network Places(View network connections) or Control Panel ---> Network Connections. Right click your primary Network Card and click properties --- > Configure then advanced tab on top.
Checksum Offload (RX or TX for some users) = Disabled
Speed/Duplex Settings or Speed = Force 100 Full Duplex (On older machines you may need to use Force 10 Full Duplex)
Optimize For = Throughput
Save or Click ok, your PC may wanna restart or your Network connection may reset.
I got a 250ms decrease in latency over Nukecap with these settings, they do help =)
Hope this helps you lot