I am sure you know since you have owned BMW's before. But maintenance costs are going to be really high especially with the used M cars. You should check out edmunds long term test of a 2002 M3. They loved it but were not fond of the costs.
2002 BMW M3 Long-Term Road Tests Blog on Edmunds' Inside Line
They also have a 370z in their stable.
2009 Nissan 370Z Touring Long-Term Road Tests Blog on Edmunds' Inside Line