No problem. 400 isn't good, but it isn't terminal. Just means you are a half second behind.
I just ran through Dalaran at two resolutions, trying to get some idea of cpu/gpu changes. But my gear is so different from yours, and its not a raid situation.
I'd suggest you run task manager (alt-ctrl-del) in Dal, and in a raid. Periodically alt-tab and look at cpu utilization (Performance tab) across the four cores. If the graphs show you were maxed on one or more cores, your gaming would be improved by a faster cpu. (cpu utilization will drop dramatically once you alt-tab, so you need the graphs)
Second, Start toning down the graphics options and see what improvement that yields. Reduce shadows, multisampling, view distance, particle effects in that order, one at a time, and see what if anything helps. (Game Menu/Video/Effects) Then put them back where they were and set your screen resolution to 1680x1050 wide. Then repeat the shadows, multisampling, etc drill.
If you get decent gains in FPS as you reduce the load on your graphics card, a graphics upgrade will help. If you don't improve much, even stepping down to an even lower resolution, your problem is cpu.
Hope this helps.