I want to keep this for six years, so in 2012, I wont have to buy a new PC.
You do know the current year is 2009 so if you plan on using this for 6 years you won't have to get another comp until 2015 or maybe even 2016 depending on when you actually get this thing built and if it still meets the specs for what you want to do with it by then. With the way the computer industry rapidly advances it is kind of hard to say whether or not a comp will still be fit for purpose six years down the road
What do you plan on doing that will require dual monitors?