Lad I know has the 2.2 SE. Feels very solid handling and feels quick, seems to have a decent amount of torque low down. So i can only presume that the 3.0 M Sport is far better in every way. Good upgrade mate, very nice indeed.
Cheers, there's quite a few different engines in the Z4, only really poor one is the older 2.0 4-cylinder with 150ps.
Pre-facelift (up to around 55-plate):
2.0i 4-cyl 150ps
2.5i 6-cyl 190ish I think
3.0i 6-cyl 231ps
Post-facelift (06-plate or so onwards):
2.5i 180ps or so
2.5Si 215ps or so
3.0Si 265ps
I can't remember where the 2.2i fits in but it's a 6-cyl 170ps and is related to the earlier 6-cyl engines like mine, but is supposed to be very smooth with a nice sound but just lacking the outright grunt the car deserves.
They are quicker than you think also.
I tried it on once in my 182 and got analy abused
Mine's a pre-facelift 3.0i: 231ps, enough for 0-62 in 5.9s and 155mph limited, but still around 30-32mpg...