No doubt i'll be corrected if i'm in wrong but i think you'll find that a stock ST4S is more powerful than the equivalent 996 anyhow even though they share almost identical engines. Its all to do with exhaust routing.

get a lighter pillion! Cheapest way to get acceleration! (maybe):devil:

I've got the ST3 and this is more than fast enough for me and that includes having the wife on the back!140mph indicated on the clocks riding to Brno last year was ample especially loaded down with everything the good lady insists on bringing with her!

I suggest if you want to go faster you've bought the wrong type of bike, after all it's a sports tourer. ...perhaps the new 1400cc Kawasaki might be more to your liking!