PSU question.

Dear God in Heaven above, do not buy that Coolmax unit!

That Corsair unit is just fine for a 7870 (has the PCIe connectors you need) and is almost infinitely better quality than that Coolmax trash. The Builder Series isn't the greatest either, but Coolmax shouldn't even exist.

Edit: 6+2 pin just means that it's a 6 pin connector with an extra two pins separate if you need them for an 8 pin connector. No issuse there.
 
6+2 is compatible with 6.

It comes as an 8, but you can see a line in the connector where you are supposed to break the two end ones off and just leave those 2 pins hanging off in space while the other 6 are in the port.

The CX600 is more than enough to handle the 7870 in general as well.