GPU Question: What is your monitor resolution you will be gaming at? If you are looking at 1920x1080 or higher, the 5850 makes sense. If you will game at a lower resolution, the 5770 or 4890 (better performance) makes sense.
RAM Suggestion: You will want a 3x2GB setup for 6GB. You will have no benefit in gaming with more than 6GB. I recommend the G.Skill PI DDR3 1600 6GB Cas7 set
HHD Suggestion: I would go with the Samsung Spinpoint F3 1TB hard drive
over the WD Black. The Samsung is the faster hard drive.