German tech site ATI Forum claims AMD will introduce the 40nm RV870 GPU with DirectX 11 support in July 2009. It's said the RV870 will offer significant improvements in idle power consumption.
The site claims the RV870 will offer a computing power of 1.9 teraFLOPS, compared to 1.2 teraFLOPS offered by the Radeon HD 4870 (RV770). There will also be a dual-GPU version of the RV870, with higher clockspeeds that model should be able to touch the 4 teraFLOPS mark.
Unless ATI changes it's naming scheme, these chips will likely be named Radeon HD 5850, Radeon HD 5870 and Radeon HD 5870 X2.