It's not getting a booster V10. I work for BMW, and believe it or not they give us lots of details about upcoming changes to models, even years in advance, such as the 2011 model Z4-M roadster, which will have a twin-turbo I6. Certain info isn't shared, but we got a newsletter last week that shows what they have in works for next year, and the info on the 2011 5 series is in there, re-designed from the ground up, but the M5 is getting a V10, not booster in any way.