The 4870 X2 delivers 2.4 teraFLOPS and has a memory bandwidth of 230GB/s. The Radeon HD 4870 X2 should be available real soon and indepth reviews will hit the web pretty soon.
Next month AMD will introduce a cheaper dual-GPU card based on the Radeon HD 4850. The ATI Radeon HD 4850 X2 is rated at 2 teraFLOPS and has a memory bandwidth of 128GB/s. You can expect to find this card in September for around $399.
The price of NVIDIA's GeForce GTX 280 flagship is now around $449 in some shops.