I'm able to five-box fairly well on my system.
Which is not as nice as your system will be.

I have an i7, 920 at stock speed.
This is close to a 930, with the newer numbers.

Similar motherboard, x58 based Asus.

I'm using a 1GB GTX275, for the video card.

I have 12GB of DDR3, also at 1600mhz.
8GB will be plenty for five boxing warcraft.
Warcraft usually caps out at 1GB per client, plus less than 1GB for the OS.

I've got my OS on a Raptor hard drive, which is a little faster at 10,000rpm.
And have warcraft on a low-mid range SSD (Patriot Torq 64GB, 220mb/sec read).
A low end SSD, purely for the gaming folder would be what I would look at if you wanted am improvement; does not have to be now, very easy upgrade in the future if you want better performance.

Similar case, Antec 900.
Lots of airflow, love the huge fan at the top and all the interior space.

I've got an 850W power supply.
But 750W will easily be enough.



Warcraft is more processor dependent than video.
If you have enough ram (and you do), then processor is generally the most important piece.
Yours is faster than mine.
You'll five-box fine on that system.

I'd take a look at the 2500/2600k processors.
Not sure if they're within your budget, but if you're doing a new system... worth checking out.