Having recently feted the arrival of the new M5, BMW M fans have another reason to celebrate with this all-new, Z4-based M roadster. The last iteration, spawned from the Z3, impressed us with its raw speed, but it lacked sophistication and was diabolical to drive fast. This newest version will have to offer much more in the way of panache and refinement if BMW hopes to mount a credible threat to the stellar--and recently updated--Porsche Boxster S. The BMW will be armed with the 3.2-liter in-line six from the departing E46 M3 and, contrary to other reports, will produce the same 333 hp at 7900 rpm and 262 lb-ft at 4900 rpm. Redline is 8000 rpm. Other changes from the standard Z4 include the addition of BMW's variable M differential lock, a stiffer suspension, and a more traditional hydraulic--rather than electric--steering setup. The Z4 M Roadster will accelerate from 0 to 60 mph in under five seconds, according to BMW. Cosmetically, the M roadster gains revised front and rear fascias and eighteen-inch wheels and should go on sale in March or April. It will be followed in June by the Z4 M Coupe hardtop version.