I understand that any of these situations can be highly variable. I guess I am just looking for general tactics.
Does one aim for the "attacking" driver? Tires?
Obviously escaping would be the best option and that's what I'd use a firearm to facilitate. However it seems there is a very low chance of incapacitating the driver. Case in point, I just found a year-old article about an off-duty sheriff's deputy in my area who was almost run down by a robber driving his vehicle. Despite poking numerous holes in the vehicle he came very close to being hit TWICE without giving the attacker a single scratch.
Of course our Sheriff's department is somewhat of a joke.. Not long ago a deputy responding to a burglary somehow allowed the burglar to escape in his (the deputy's) SQUAD CAR.