You can do > 200W on a 6 pin connector.

The 75W and 150W aren't the technical limits they are part of the PCIe STANDARD.  No miner is using PCIe slots, no miner is doing wattage interogation on the PCIe bus, no miner is doing a ground sense on pins 7 & 8 to ensure they are compliant. 

75W and 150W is utterly irrelivent to mining.


Hint:  Have you looked closely at a 8 pin connector.  What are the extra two pins connected to?