BMW always does that, they do not assume optimal weather conditions, etc.
335 is rated at 5.3 seconds, but tons of people got a 4.8 sec on it.
i was watching vid's today of M3 vs. RS4. go to youtube and put in E92 M3 and see vid's for yourself. it performs better than RS4, but in terms of 0-60 or straight line it fails vs. the C63 AMG.
there's a few good clips there, including sound clips. check em out