The 6870 is the strongest out of the 2 you have chosen.
The Zosma 960T is a nice cpu and will handle your surrounding hardware nicely.
For a psu i would suggest a decent 650watt psu.
One of these:
Antec Earthwatts Green 650w
XFX Core Edition 650w
PC Power and Cooling Silencer MKIII 600w
Find all these great PSU's here:http://www.newegg.com/Product/Product.aspx?Item=N82E16817703036