One of the first things I noticed was how much quieter it was inside the car. And as far as heat, I finally got my heap together in Oct. so it wasn't really all that hot out. But there was a noticeable difference in how warm it WASN'T inside the car from the exhaust.
100 sq. ft. is enough to do an entire floorboard and inner roof on a fastback. First I coated the floorboards with POR-15. Pint can did the entire floor.
Then I applied the FatMatt everywhere including around the wheel wells since they looked like they'd amplify noise behind those big side panels.
I bought a 100' roll on e-Bay for about $100 shipped to my front door.
Just make sure you measure where your seat belt holes are BEFORE you apply the mat. I didn't do this on my headliner and it caused me some anxiety installing my shoulder belts!
BTW: I just recenly found some OLD pic's of when I first got my car....
Look at how big those damn bushes grew! THAT'S how long it took to get the restoration done! :-D