I have to eliterate my comment from months ago, about weight not effecting top speed, normally it would effect the top, but putting a certain amount of weight on a car would, like for instance if the Zonda was 30,000Kg heavier...it wouldn't reach it..but of course no car would have that, my point is a bit moot, but realistically, it weight would at some point given enuff.
And even how quickly it gets there may not be totally right, weight as a whole maybe, but with the advances in tech, Power To Weight Ratio isn't the same, no matter how you look at it, Corvettes, 911s, GT-Rs, they have changed that big time.
Question is, will PTWR ever be obsolete regardless how much or less Weight/Power? I think it will someday.