5850 won't play all games at max settings at 1920x1080. The 5970 will, it'll also last the life of the system.
RAM wise go with the ripjaw kit. If those that's the Mushkin kit I'm thinking of it's 1.75v, which is a big No no. Also, if you aren't comboing, the ripjaw and eco kits with same speed/timings are same price. Eco's are better due to same performance at much lower voltage.
overall build is fine. Monitor wise decide if you want HDMI or not, that + slight size variation is basically the only difference for monitors in the price range $150-$200.
You don't need a 1366 system unless you need to actually use software that's well threaded (most common are rendering, encoding and filters in Adobe products).