Most of everything mentioned above is accurate. The term "car to car" is 99% of the time going to refer to officers talking on a simplex frequency or " around the repeater" as its called where i live.
As far as range, just like anything radio related, it all depends. I've called other units on a simplex frequency approximately 8 miles away before. That being said I had a 50 watt VHF car radio with a 3db gain antenna. I don't know whether it would reach out further or not, never had to try it. You have to figure though, real-world range on these bubble-pack GMRS radios is over 3 miles and thats with 5 watts and a small antenna. Take 50 watts and a high-gain antenna and the range is going to increase.
Just an FYI, the car to car channels are the ones to monitor if you want to hear more "un-professional" talk on the radio. THe car to car channels aren't usually recorded by dispatch and more often than not aren't monitored by them either. There is always some good listening to catch on these frequencies, but you do have to be within "reasonable" range of them.