hmm I never owned a SSD, but I do know that Wow(thats what you are playing now correct?) uses random read/writes, so SSD will improve that speed with loading and what not.

If I was building a system to 5-box, i would just save until I have enough for all the parts. This way you can get an amazing system that will not need to be upgraded for a couple of years.

But if you want us to post a nice system for you, we will need how much your budget is.
you can builda dual core system for cheap or a quad core for somewhat cheap, but you might be better off just building an i7 system for around the same price as a quad core system.