It sounds really odd, but for that reason alone (a wreck) I don't like topless cars. I mean I like them to look at, but not to drive in. I guess I am just weird. I had a guy run a red light hit me/friend head on (she was driving) doing about the same MPH and we ended up with physical therapy for about a year, not cool at all. Wasnt in a mustang, but the card held together. The only thing I can say for the angle that dude hit you is that Ford made some good heavy doors to hold that impact on the side of the car. When we got hit, they had clipped the front left of the car, bounced off us, landed about 30 feet in a sideways direction and we were pushed about 5' back.
Good on the 99 also, when I get one if it can not be brand new, I am thinking between 99-01 since Im not super fond of the other "slight" body changes.
