I used to have a 52 plate Z3 2.2 sport, which i bought from new. I can honestly say in the 3 years that I owned it, it was the best, most fun car and most reliable car I have ever owned.
Not only did I find the insurance and servicing very reasonable - not something I was expecting!
I haven't driven a 2.8, but thought I'd share my love of the 2.2 with you ;)
Hope that is of some help!
Nina