Fun decision to make. Are you planning on doing a lot of highway driving? That may give the edge to the M5. However, as pointed out the F90 is at the end of its life cycle while the G80 is at the beginning. The G80 is certainly big enough for most people (its as big as my E39 M5).
Overall, I'd give the edge to the M3 given all of the above. Now what would
I do? Order a manual G80 for approximately $75K instead of the overpriced (IMO) 50 Jahre with its $10K dealer markup (
).
GL! No regrets either way.