+1 about the 9800GTX. Not worth it until you can see more information about the 4850/4870. I've already actually seen some numbers already that shows amazing performance out the 4850.
Get a powersupply from a more reputable company like Seasonic, PC Power & Cooling, or even something from Corsair. 550-610W would be perfect for years to come too.
The reputation thing comes into play with that RAM. In experiences, I've found that G.Skill makes ram that works, it doesn't OC particularly well, so that might be an issue for you? Check out Crucial Ballistix, Corsair XMS2, or OCZ Reapers.
About the case, have you looked at the Cooler Master 690? It's not much more at all.
Getting to 4GHz is luck as much as anything, but it is going to require a better PSU than what you have. We are telling you this because its true! The PSU is the ONE area you do not cut back on due to budget concerns. Cut somewhere else.
48x0 will be out soon. 2xx series is out Wednesday.