it doesnt need 8 pin.
the spec has been 150 watts on the first PEG since PCIE 2.0 introduction.
The extra 2 grounds on the +2 are just for resistance reduction and sense.
unless you are using a crappy pre-pcie 2.0 power supply, then you might be in trouble.
not to mention the fact that AMD has wired up the traces on the peg connector to contain the two extra grounds.