I have fairly regularly put my car on the drag strip as I only live 5 miles from Santa Pod.
There are some on my webpage
http://www.baldrys.co.uk/Botang.htm
my best time at Pod in the stock 4.2 A8 is 15.01 seconds so 14.77 in an S8 souns about right.
In my experience winding up the gearbox by holding it on the brakes gives you a slower ET, as does messing about with tip, sounds like you did exactly the right thing.