This is from "Auto Motor und Sport TV and a episode with a comparison between the M5, the RS6, and the Alpina B10.
The video is about 15mb and hosted on someone's home server, so it won't be up for long.
Please right click, save as instead of trying to watch it streaming
and it may be up for a little longer
http://www.szetofamily.com/m5/M5Compare.wmv
It's the usual story though: you see the RS6 win the acceleration, the braking etc. but who ends up winning?