Because these supercars are designed to handle their given power in all gears ( not to say you can't overwhelm them though) a zed on the other hand isn't designed for 660bhp!
But I get there's arguments for and against and as you said I would rather have more power and use less of it , rather than not have enough . There must come a point though that any more bhp in a zed , on the road is pointless?