Takes 16v engines a little longer to get to the optimum point for air/fuel to create the best power. They have 16 valves but are smaller than the valves on an 8v engine. IE when you open an 8v up is should be letting pretty much all of the air/fuel in imediatley. But the 8v runs out of puff earlier and cost it. Also the 16v is more efficiently timed.
All 16v are DOHC and use one for inlet and one for outlet, I believe you can have 2 different profile cams to do something, would assume one is to free up exhaust gasses more efficiently?
VVT I believe is to optimise low range power and top end power, IE keeps the delivery smooth at nearly any revs.
Williams should hit 85% of full power at 2,500 rpms so no need to wait for 4k!