Season 8, Episode 4 Richard tests the Z4-M and compares it to the (new) Porsche Boxster. Is this the episode you're looking for? If so, here's the YouTube video: http://www.youtube.com/watch?v=4E2ooCkW4jI The only other thing they did with the Z4 to my knowledge was Season 3, Episode 2, where they compared the BMW Z4, Honda S2000, and the (older) Porsche Boxster. The Z4 in this episode is the standard, non-M version.
Thanks thanks I found the video It was the TopGear 24-diesel Endurance race video. The z4 mcoupe was blue red bull sponsor http://youtube.com/watch?v=1LUgwvVHosU