Nice chassis. Yeah, this card will get you decent frame rate at 1920x1080, no AA. The AA always drains my FPS and I have the GTX295. I should of gone with 2x BFG GTX275. This would of outperform the 295, and cost the same, and than just run a 3-way later on. There is a good chance I would just go quad with a second GTX295 someday. You just might always go with one real fast card, rather than investing on PSU, MOBO and a second 5850 , like you stated. At one point, thats what I did. Best of luck on your future upgrades my friend.
p.s. How is the 5850 performing at 1920x1080?