I bought my Z4 in July after having just come to an agreed price on a H2000. The Honda came out about $6,500 less but there were some issues. The H2000 is basically designed to simulate a race car. It has virtually no creature comfort amentities. It doesn't even have a glove compartment. The cockpit lacks space to store anything bigger than a cigarette pack. The trunk is very small although I could fit my golf clubs as long as I didn't want to store anything else there.
The low-end torque is troubling. In a test drive, it felt more like a Mazda Miata until you got above 6,000 rpm. Since most cars I'm used to redline at that level, it would require relearning how to shift and drive.
I haven't had one moment of regret with the Z4. I'm not sure about the Honda, but the BMW's DSC and DTC in the severe winter we are having here have been nothing short of sensational. It also handles like a dream in good weather.
I also heard that the H2000 Original Equipment tires only last a few thousand miles. Different tire sizes on the front and back also complicate things.
The Z4 is a great high-performance sports car which doesn't lack for amentities (many of which are unavailable on the Honda). If you want to race, perhaps the H2000 might beat the Z4, but not by much. But how often would you do that?