I went from an E39 540 to an E60 M5 a few years back. It was long awaited for and nothing short of my dream car. However, it's a maintenance nightmare. Lot's of SMG issues, none of which are cheap. I dumped it after less than a year. I would buy another but never as a daily driver. The car is simply amazing all around at full throttle. At that moment the SMG Tranny makes sense but putting around it sucks.
Hope this helps.