You might want to consider the new gen of Trinity APU's instead of A8 3870k, something like the A8 5600k has about the same CPU power but will be using a new platform you can upgrade later. If you're going with a discrete card like the 6870 you should consider the pentiums or an i3. The A8 5600k can work well with a discrete card but pairing it with a 6870 is a bit wasteful. If the price is good then buy all means.
Here is what I have come up with
Its a a8 5600k (close cpu performance to a FX4300, slower by 200mhz (cna OC the difference)
Has a 7850 1gb (pay about $10 for extra 1GB) and 1TB of storage http://pcpartpicker.com/p/rrPS
This one is the FX6300 with a 2GB 7850 but only has a 500GB hard drive, you cna get a different one if you want. You can swap out to a FX4300 for $10 cheaper which can still for the most part outperform a i3 3220 http://pcpartpicker.com/p/rrS8