You are really comparing top end single computer multiboxing to low end multi computer multiboxing.
I have a Q6600, 4GB ram, nvidia 8800 GT, couple 7200 SATA hard drives and it is fine. Probably could do with a another 4 GB of ram when I hit northend (I level really slow :-)), so anything over that it will be good. I7 and all other components that you list is overkill, and that is ok if you must have top performance with top graphic quality and don't mind paying the price.
You should be able to multibox just fine with a $1000 computer.

Edit: should have used the preview button first ....