The main thing on the M5 buyers guide is the clutch and flywheel condition.
I will sell in 3,000 miles with a practically brand new one. Has to help the resale value.
Won't hurt it,put it that way,but you know what the resale value of these cars is like currently.
500bhp and < 20mpg is one thing,and 500bhp with 30+mpg is another.
All I'm saying is I'm sure it was fun,but it sounds like you've had enough of it.