AMD has a secret weapon called side port memory. We wrote about it before and it's the memory that will up the internal chip bandwidth from 6.8 to 22GB/s.
This is not enabled at launch, but it will be at a later date. A cool manager called Ian McNaughton said to the world that this performance will only be visible at synthetic benchmarks and not in games.
AMD also showed a demo where Radeon HD 4870 X2 beats Geforce 280 GTX OC edition in Call of Duty, 3D Vantage and Lost planet by more than 10 to 20 percent.
With two Radeon HD 4870 X2s you can get slightly above 30FPS in Crysis; while two Nvidia Geforce GTX 280 gets you roughly 10 to 11 FPS. This is quite an achievement.
The only bad point is that Radeon HD 4870 X2 is more expensive than GTX 280.