The second build (with the Q9400) is not bad either, but if involves expensive DDR3. Also, the Phenom II 940 trades blows in gaming benchmarks with the Q9550, and the Q9400 is weaker. I don't like the Q9400 because it has a low multiplier and small cache.
If possible, upgrade the HDD to WD 640GB Caviar Black (WD6401AALS).
Probably about $200-300 under budget.
I went with the 720BE over the 940BE because there is no real difference in gaming between the two and when games do take advantage of multithread more the 720 still has 3 cores. http://www.anandtech.com/cpuchipsets/showdoc.aspx?i=351... Benchmarks in games.
The system will allow you to crossfire two 4870s down the road. In a years time they should be around $100 mark. The Biostar board can be swapped out for the Gigabyte board at the cost of ~$45. To me its coke vs pespi or no-name vs coke etc. The user reviews are good for the board with the exception to board layout if your crossfire you'll have access to 1 PCI slot.
Heck, if your a gambling name the 720BE might have an unlockable 4th core anyways (although the chances are slim).