Here's someone who has put together a parts list who updates it depending on prices and new releases.
http://forums.ncix.com/forums/?mode=...nt=3&subpage=1
You may want to upgrade the CPU to an i7 and as you say, the memory. From what I've looked at all the newer top GTX cards support 4 monitors through HDMI, DVI, and DP but check out the outputs on each brands models as they have different combinations.
also google "computer build" and you'll find a few sites that give options for your price range. Set your country as Canada and know that NCIX and Memory Express will mostly price match your components.
Also
shopbot is a good place to look for the best prices.