Assuming that what I heard was accurate, and depending upon what % drivetrain loss one uses as an assumption, the crankshaft horsepower would probably be somewhere near that range.
Again, I am simply repeating what was told to me by what appears to be someone with much more information as compared to what the general public would have through the internet or other publicly-available sources. Then again, my source could certainly be mistaken... guess we really wont know until people start to dyno their stock F10 M5's!!!