Dragon platform advantages for ATI vs. nVidia?

The news about AMD's top-of-the-line Dragon platform is all well-and-good, but what does it actually mean?

I currently have an AMD Phenom 9600 BE, and was looking to move to the Phenom II, since the old B2 stepping that limits my 9600 makes the OC'ing ability nigh worthless. I am considering both the X3 720 BE and X4 940 BE. Both seem to clearly beat my current CPU, and both can be OC'ed about 1Ghz or higher on air cooling.

My current motherboard is a 790FX (MSI K9A2 Platinum), so that would be fine. I was thinking about getting ASUS M4A79-T Deluxe for the AM3 socket though.

My big question is the graphics card though. I know that a ATI 48xx graphics card completes the Dragon Platform. But will a nVidia card work just as well, or will I lose out on performance that a similar ATI card would give?
I currently have a MSI NX8800GT 512Mb. While this certainly isn't the best out there, it IS a good card, and I haven't had much for difficulties with it. Compared with the Sapphire Radeon 4870 HD 1Gb, would it be worth the extra money to switch over? Am I really going to see a massive performance jump?

What advantages are there to using ATI cards vs. nVidia cards in a AMD setting, specifically Dragon Platform with 790FX/Phenom II?