I can guarantee you that there is not a single 470/480 out there that uses 25watts of power thru the riser. Any 6 PIN GPU usually uses about 45-70 Watts from the PEG connector.
The only GPU that I measured that used 25watts from the PEG connector was a ASUS 7970 which had 2x8pin slots to get most of its power from.
The Gigabyte G1 uses 44Watts from the PEG
The MSI 470 4GB uses 60 Watts from the PEG
The MSI 370 OC uses 70 Watts from the PEG
PEG = PCIe slot power / riser power
So, you wanna say that my G1 uses ~40W from Extender out of ~90W total power? What about cards connected via only cable riser?