As for the extreme cold question, I'll say I never had any problem. This past Feb it got well below freezing for a while there (my FE dropped under 30 mpg for a tank, a pretty big hit), but never had any problems with the car, starting it, running it, anything. Engine braking isn't quite comparable to downshifting but I don't remember what I've read about the mechanics of it to really give much more. At least not clearly. With my half clue I could maybe give you a quarter of a clue, hehe.