I just bought a BFG Geforce 7900GT OC 256MB PCI-e on ebay. (Please don't tell me how obsolete it is, because I got it for $26.) I just found out that it does not come with anything other then the card. The card has a place to plug in a 6-pin connector, but I'd have to go buy one separately. I know that they are sold for only $5, but I was so proud of the low price I paid for the card.

So, what would happen to the performance of the card without the 6-pin connector? Will it cause worse graphics? How important is the 6-pin power connector on a BFG Geforce 7900GT OC 256MB PCI-e Video Card?

I'm pretty sure the card won't even run without it, so you will need that adapter.

Without the plug, you've got a new $26 paperweight. Get the molex to 6-pin adapter.

haha yeah just grab an adapter. my old x800 pro wouldn't boot without it. it made a loud beeping noise. another 5 dollars for what you're getting is still really really good.

Yeah, if the plug is given, it won't work without that connector. It's needed for the extra power. PCI-E slot can provide only 75w, PCI-E 2.0 150w , pci-e 6 pin connector 75w and pci-e 8 pin connector 150w. Depending upon how hefty is the power usage and few overclocking margins, additional power connector is given.

If the card has a pci-e power in connector...then it needs it.
If you don't have one...skip getting the four wire to six wire adapter. Get an ATX12V 2.2, EPS12V power supply.