[Molez93]

Wow. Two completely different vehicles... as if you didn't know.
Have owned an '06 Z4M R since new. Had an '01 M5 for 4 years from 2011-2015.
They're both impressive in their own ways. I'd probably still own the E39 if my wife had *any* interest in being a passenger in it. Ignoring her opinion, I still like owning the Z4M much more. My experience with it has been essentially free of any- no seriously- any mechanical issues. Could be that it's limited to occasional summer duty now and only has ~35k miles on it. The M5 was a money pit the entire time. I think I averaged $3-4K/year in parts which failed (from 102k thru ~123k mileage). I'm not even counting the $10k+ I spent upgrading the *entire* suspension to make it handle less like the heavy boat of a sedan it was. The M5's body roll in stock trim was disappointing. Breaking tires loose without trying during the 1-2 shift was pretty sweet. :-) The rather intrusive DSC/traction control is annoying in both, but especially so in the M5.

I'm sure your research has given you a good idea on the care and feeding of each depending on the miles on the odometer. You'll have a sh1t-eaten grin on most of the time with each as long as you're not lamenting the damage to your wallet along the way.