Ehm... what about handling? BMW vs Nissan?

I'd say they're similar in overall grip. The Z might have a slight advantage in handling at the track being much lighter but still not enough to overcome the power disadvantage to the M in lap times. From my experience in the bmw, it seems much more poised when driven hard and has quicker steering input. I think most mags have the Z's lane change speed a little slower than the M's.

i think they weight approx the same.

BMW M3 weights about 1550kg withouth passenger and with full fuel tank..

You might be referring to the E46 m3 last gen. The new V8 m3 weighs around 3700 lbs or 1681 kg. At most the 370z weighs 3350 lbs or 1522 kg and thats being generous. I have a base model which autos.msn has at 3250 lbs (1477 kg). Its not rocket science to assume a german v8 semi-luxury passenger vehicle is going to weigh more than a 2 seater japanese sports car. The Z isn't an rx-8 or honda s2000 lightweight but it certainly has a weight advantage over a new m3.

dont want to argue but it doesnt, bmw says 3700lbs but the real weight is less. :hello:

I have no problem arguing. It's impossible for the new gen. m3 to be the same weight as the last gen. The last gen. m3 weighed right around your estimate for the new one at3400 lbs (1550 kg). The new V8 weighs slightly less than the previous inline 6 and employs carbon fiber but not enough to offset the bigger heavier bodystyle that bmw went with in the new 3 series lineup let alone all the technology added into the M version.