the X3 is available in five different engines: 2.0i, 2.5i and 3.0i for fuel, and 2.0d and 3.0d for diesel. (automatic gear only on 2.5i, 3.0i and 3.0d)
Don't know about the 2.0i, but the equivalent 2.0d (150hp) can easily, safely, and really quickly, go up to 180km/h without noticing, but after that there's still engine but you start feeling less secure. Once I hit the 200km mark, but there was too many cars around.
Like B&DCalgary said, unless you live in Germany, it really doesn't matter because most highways are restricted to 120/130Km/h.
We do live in Germany, but we are Portuguese, and Düsseldorf to Belgium is half an hour, and belgium border to Portugal are the biggest part, so we won't need high speed at all.
For low revs, the engine can easily go down if not accelerated at all (e.g. climbing simple a step from the road to the place people walk), , but it's enough to accelerate from 1.000 rpm to 1.100 rpm to have an engine capable of anything you feel like to do
And from September onwards, the X3 will receive the new E90 2.0d engine, with 163hp.
I've never had so much fun with a car
)))) I'm sure you'll also have fun with the 2.0i, specially when filling up the tank. (I've done 8l/100km this weekend)