Not sure where your getting your information, but the HD4850 basically shares the HD3850 PCB and thus it has a 6pin PCIe power connector.
The HD4850s were/are on sale as a guy over at XS has one. He kindly has done up a review:
Vision Tek 4850 review - XtremeSystems Forums
It should surpass the 8800s. It comes pretty close with the 9800GTX from what I've read. It's not a top-card though, this is a mid-range card so you need to keep that in mind. The HD4870X2 will be ATI's top card.