Higher FPS in a raid means higher DPS and better reaction-time to events.
FPS: here is a new addon TweakWoW which lets you tweak settings (including a reduction in Dalaran lag, worked for me) that are normally hidden in the wtf/config file. A recent version added support for multi-core CPUs and I saw a massive speed boost on my Intel i7 920.
Latency: these tips improve latency but they might have other consequences (but didn’t for most people whose comments I’ve read). Very effective if you’re a high ping in say Australia to the US servers, but also works here in the UK to improve latency. Reports of reduction from 200ms to 50ms. They’re basically getting around the Nagle algorithm.
Thanks to my guildies for the latency links.
Lowerping.com: more effectively albeit a paid service (AU$20 for 3 months for US servers), you can use lowerping who provide an improved latency for Australian, Latin American, Japanese and other regional players who are on US or EU servers.
Playing on US server from EU ping went down from ~400 to 180 to 200 ms in-game.
I have a full written review on lowerping.
Profiling: to profile your CPU and memory usage, to look for hogs, I use BrokerCPU coupled with Fortress to give it a GUI. I found that Big Wigs, AG Unitframes and Recount were using more idle CPU than I’d like (not that’s a huge problem). I swapped them all out for oUF Caellian, Skada and DBM. Most recently I’m testing Shadowed unit frames and they’re quick too. Bartender is using idle CPU too, so I swapped it for Dominos.
I’ve heard Pitbull Auras are/used to be a terrible CPU hog, and that Dogtags can be too.
DNS: I also found switching to OpenDNS helped general internet speed. It’s free, took about 3 minutes to set up; just changed to a manual DNS setting on my ADSL router.