Remember there's two engine sizes, and the offer seems to be for the 3.0. I've driven a 335xi and Z4, and the Z4 was certainly more "frightening", but in a good way... I went for the 335, my wife "commandeered" it, so I'm about to jump on a Z4 too!!!
I'd definitely do a test drive, but only after you've run the numbers to see if you can take the hit!