Ok, Well get the e6700 if you have the money. Also if you are not going sli don't get the 7960g2. It is just a waste of money. Get a x1900xtx or better yet x1950xt. IF you are going to get directx 10 cards when they come out. Go for a 1900xt and save a little money for you gpu upgrade. Great high-end system. I just wish I could get the E6700. It is too pricy for my blood. Also you may want to consider waiting a month or two for price drops.
the 550w may be fine for now and a year maybe two. I woud go for a 650w or even a 700w becasue you plan to upgrade. You may not need all that power but more is better.