You'd be surprised how much difference that extra horsepower can make. Just look at the Veyron. If I remember right, it only needs a couple hundred horsepower to get to 130 or 140 MPH, but it needs the extra 800 horsepower required to get up past 200 MPH to overcome its own coefficient of drag.
Either way, its hard to give a solid answer when you arent really giving us specifics here lol. "...something like 20 seconds", and "about 30 seconds" is a very big difference lol. Find the exact numbers and it might be easier to go from there
Oh, and in a choice between exotics, I'd probably take one of these:
