The April issue of Bimmer Magazine has the M5 on the cover, with articles comparing the M5 with the 550i and Z4M.
The articles are posted online:
http://bimmer-mag.com/art1/art1p1.html
http://bimmer-mag.com/art2/art2p1.html
The articles are posted online:
http://bimmer-mag.com/art1/art1p1.html
http://bimmer-mag.com/art2/art2p1.html