Agreed more RAM for your buck vs. 2 video cards in SLI mode you wont need it anyways. WoW is not exactly a graphic monster of a game and RAM dedicated to each window would be good, even if you do get 2 video cards you dont get anything from SLI'ng them for the purpose of WoW you can just have 2 cards for up to 4 monitors.

GTX280 is a definite overkill go with the 260 not as beefy but for WoW 260 is just a step down from the 280 so you wont lose much and will pay a whole lot less.

Again on the RAM as suggested go higher end DDR2 you will not really see much of a change when talking WoW unless you are doing something else that requires you to have the higher end DDR3 then you dont need it.

These suggestions will bring down the price of your over all system, it alreayd looks like a monster of a gaming rig with what you have planned stepping down some of them and saving some money will allow you to go with the 2 video cards.