Well, there are 2 different known attacks:
1) relay - it doesn't care if the keyfob is 40, 80 or 8millions bit. It simply relay the signal from your keyfob to the car when you are not near the car. The attackers need 2 piece of hardware: a receiver (to be held close to the keyfob) and a transmitter (to be held close to the car); receiver and transmitter can be miles apart. Well known attack in Europe, less frequent in USA. This is where removing passive entry, and activating Pin2Drive will prevent such attacks. (this is valid for any car with passive entry, not only for Tesla)
2) keyfob cloning - this attack has been demonstrated by a group of researcher, but there are no reports of it being used in the wild. Here an 80bit fob will make the difference to a 40bit one. With such an attack the attackers can "clone" your keyfob and use it as they like: they will have a copy of your keyfob. In such a case disabling passive entry will do nothing to protect you. On the contrary, activating Pin2Drive will still prevent the attackers from stealing your car (but they can steal what's IN the car if they successfully clone the keyfob).
I'm sure someone posted a picture of an open 80bit keyfob, to show how to tell it apart from an 40bit one looking at the part/serial number, but can not find it atm.
. I have an annual service tomorrow and have also asked for the new fobs to replace my existing ones, so I will ask at the SvC. Perchance someone else may provide the answer before then..
