I just got my 135i about 3 months ago and think i can answer this question. The 135i is clearly a quicker car than the 03-06 350z, no doubt about that. What we need to worry about is the 07/08 Z's with the HR motor. My brother in law has an 07 Z and from a dig i take him every time. The HR cant match the 135's 1st and 2nd gear grunt. From a highway roll its a different story. He pulled on me every time because the HR really starts making power from 5k to 7.5k unlike our cars. Stock HR's have also been known to run low 13's in the 1/4 mile and trap at 106-108mph, definitely no joke.
Both our cars are stock 6 speeds btw. I found this video on youtube and this is an accurate of what happened to me.