I think it comes down to mastery of the tool. The 335 is easier to jump into, drive fast and control at the limit. The z4m has greater potential on the track but it takes time and greater ability to master.
The z4m reminds me of the s2k in some respects, more of a driver's car with quick responses but it can be harder to control and twitchier at the limit due to its shorter wheelbase. Regardless of what the article says, I would definitely rather have a z4m on the track.