Great questions (and my phone lost my first response... So this one will be shorter)
Ex/exl chassis vs l chassis -- I haven't gone back to back with the same setup yet. I suspect it will really be a fine tuning like change. On asphalt I believe the preference will be ex/exl due to rear bite. At the Reedy Kyle ran a A700EXL and Austin and Aaron ran the A700L -- they where the same speed -- fast!
#3 dampeners -- I ran them in Florida at the ROAR Nats. To be fair, I was still figuring out the car and how to tune it back then. In the heat of the sun I couldnt get the car to stop feeling springy. In the morning/evenings the car was really good.. But the change during the hot day wasn't something I could keep up with. The #3 I think will be very good indoors when not hot and outdoors in low grip scenarios.
I'll defer to Oleg or others on why folks are running am18 vs am19.