Prior to the CES craze, revamped 8440w and 8540w notebooks were spotted and an HP product manager said they would exclusively offer Nvidia graphics. HP officially unveiled the updated EliteBooks at CES, and along with Intel's latest processors, USB 3.0 and other goodies, the systems were said to use next-generation Quadro GPUs.
Based on the recently discovered document, the EliteBook 8540w (and perhaps others) will be configurable with a GPU from ATI's new workstation-class notebook graphics line. HP Fansite speculates that the FirePro M5800 is derived from the Mobility Radeon 5830 or 5850 and has 1GB of DDR3/GDDR5 RAM.
If interested, you can read the EliteBook 8540w Maintenance and Service Guide here. ATI's FirePro M5800 is mentioned many times throughout the document.