I saw a black one in Chicago today. It was pretty sick looking. Why does it have less power than the old Vanquish S?

 

it's down 10 hp, but gets to it 500 rpm sooner.
it's down 6 ft/lbs, but gets to it 50 rpm sooner (huge difference, i know!).

i haven't driven either (but i'd love to!), so i can't say how the engines behave differently. but i do know that Bez was saying the goal with the DBS's engine was not to be a high-HP peaky race engine, but to be a more tractable, all-around useful engine.

maybe comparing the dyno plots of the power curves of the two engines would help shed some light on it? (a quick Google search didn't pull anything useful up to use for comparison).

but it could be a lot of other things that make differences, such as engine response (lighter components, for example), fuel efficiency, CO2 ratings, etc.

 

From what I have read drive the 2 around the same series of curves and you will tell the difference - more so w/ a non-S. I have not driven a Vanquish S so do can not offer a real comparison.