Where I live there are usually only the local drivers who come on our roads...
There are a lot of local hotted up cars (wannabes), and a few contenders.
The local "ace" has a 599GTB. He takes on everyone and wins.
I haven't seen him as yet while in the Z4, but it may get him steamed up enough to challenge (as the red mist falls over him again).
There is a F430 out here as well, but I have only ever seen it driven at snails pace to the shops on the weekend...
The only guy who has made a noticable challenge so far (and I only take off in D with half throttle - not really trying for speed, more for exhaust bark) was in what we call a Ford Typhoon on my delivery day. The Typhoon is a 4.0litre straight 6, single turbo family sedan, that puts out 310KW (Z4 is 250KW) but he weighs 250Kg more and has either a sad manual tranny or a 6speed ZF auto. Shall we say he was embarrassed, even without breaking the 4500rpm self imposed limit.
At the track on the straight, with a range of BMs and porsches there, it was only the new 911s and an M3 CSL that I had to use the overboost button to keep up with.