EVO does the comparison well showing both cars lapping at the same time. This allows some of the trademark characteristics of the cars to show. Namely that the 911 has less understeer on turn in but this is the area that one traditionally has to be careful with a 911 getting back on the power exiting the apex so that oversteer does not bite you in rear end.
The 911 handling is definitely tighter. The M4's additional mass shows as it tends to push a bit. The 911's lead built in and out of turns is made up by the M4's power. Finesse versus muscle is what we witness. The tighter the course gets, the more it ends up favoring the 991.
Laptimes (for reference a 458 Speciale laps this track in 1:14.2):
Porsche 991 Carrera: 1:17.8
BMW F82 M4: 1:19.2
The 911 in this comparison proves it is the better sports car. To open up a gap like that on the M4 even with a huge power deficit shows how impressive the 991 chassis is. If this was a 911 model with more power, it would not even be a contest.
The M4 is more muscle car and that is the direction BMW M is headed with their street cars. If you want the cheaper car with more power, the choice is the M4. If you want the better driver's car, it's the 911.