I beg to differ. The two cars are essentially the same. Having test driven both, the only glaring difference is the fixed roof and the marginal 0.2 increase. The straight 6 still delivers a top speed of 155, but with a 0.5 reduction in 0-60 time. The preference between the two extends only as far as which do you prefer - The added extras afforded by the M package, or not. Either way, both are in a different league to the 350z, and I feel no shame in saying I adored my 350z.
A z4m is not a z4 with a "m package".
It's a proper m car like a m5 or a m3. Not like a 330 with a m sport kit.
The z4m is a much more raw and has the engine from the e46 m3.
Comparing a z4 to a z4m is the same as comparing a 540i to a M5. No comparison at all. Different league.