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.