Just on your first question, London is a sprawling city, only beaten in area by New York City. However, its climate is, as you will no doubt know, maritime dominated. London is on a wide estuary in the east, not far from the continent, but suffers greatly from the urban heat island effect, raising temperatures by some degrees compared to the surrounding countryside. Essentially, sea + concrete = warm. I would say for a city of similar size to NYC the climate differences are sharp.