I have a F10 M5 and a 991 Carrera S. You can't compare them. First, from all the research I gathered before I got the 991 it was; pretty much don't bother with the 997's. The 991 has come a vast distance compared to it's predecessor. It by far is an amazing car. Coming out of the M5 into the Carrera you will be disappointed by acceleration, however handling will overshadow that feeling. I have a love affair with both of those cars. My M5 is my wife and my 911 is my girlfriend. Theres just things you can do with the 911 you just can't do with the M5...But at the end of the day, I still truly love my M5.
If you wanna hear some nice engine sounds, heres a clip from me the first time at a track with a Porsche. Tires were cold cause it was only 55 degrees out. Next time with warmer temps I will push her harder. If you're wondering why my friend is holding the dash is because he's paralyzed from the waist down and it took every ounce of strength for him not to be thrown around.
Getting acquainted with rear engine was a new a different concept for me. It is truly astounding how much that ass just sticks to the ground.