Hmm... I was looking for a bullet today actually, I'm building a collection of fast cars in the airport hangar. I've modified them all with nitro, hydraulics, etc.
I'm not sure the bullet is the fastest car though, I'm thinking maybe the Turismo (Which is common in Las Venturas) or this GT car I found in San Fiero today. I've only ever seen the one and it was parked somewhere. It seemed very fast. I can't remember where it was exactly though.
I'll check them out and give you my opinion, you could be right.