IGN reports that Xbox 720 will have a graphics chip that will be based on AMD's Radeon 6000 series. The next Xbox will ship to retailers in late October or early November of next year with six times the processing power of the Xbox 360.
In real terms, the Xbox 720's raw graphics processing power is expected to be six times that of the Xbox 360 and will yield 20-percent greater performance than Nintendo's forthcoming console, the Wii U.
Source: IGN