2500K is about the best thing you can get for WoW.
In testing it even beats Intel's 980x, which was a $1000 CPU a few weeks ago now I think it is down to about $800 but still at only $200 you can have more performance in WoW than anything else out there. I have one and I run mine at 5GHz for daily use and can go up to 5.4GHz if I want but gets a little hot since this is all on a $30 air cooler.
If you do other stuff besides play games like rendering HD video or 3D images, than the 2600K will be better all around but just for games the 2500K is extremely good for the price. I got my CPU and motherboard on the release day from MicroCenter for $368.03 after tax (CPU was $179.99 and motherboard was $189.99 then a $30 combo discount)
I would go with a 2500K and an ASUS P8P67 Pro motherboard. Gigabyte is good too but as of right now they haven't even finalized their UEFI BIOS (the one you can use your mouse in) so they are a bit behind all the other manufacturers at the moment.
If you live close to a MicroCenter you should at least buy the CPU there. They have the best CPU deals period. What they do is sell their CPU's below the cost of what they pay so that you get to the store and hopefully drop a ton more money on the rest of the parts there. There is no rule that you have to buy something else than the CPU though, so if you can resist that temptation just go in the store and get one for a super cheap price.
Unfortunately they aren't as cheap as they were right after the release but they are still $199 for the 2500k and $299 for the 2600k, which are about $40 below everyone else.