The ‘20 DBS Superleggera Volante delivers hair-raising, open-top V12 excitement, writes Road Test Editor Howard Walker. Ponder this bijou factoid for a second: The top speed of Aston Martin's new, breathtakingly gorgeous, 715 horsepower DBS Superleggera Volante convertible is 211 mph. That in itself is mightily impressive. If my math is correct, at that velocity the thundering Aston is covering the entire length of a football field in a hair over one second. No, what's really impressive is Asto...