bear in mind, simple "power-to-weight" only goes so far.
Once you start approaching/exceeding "motorway speeds" the air resistance means the more powerful, but heavier car will start to win out.
think of it as "Spare-power"-to-weight...
If you take a 1500kg S3 with 270hp, and a "matched" 1250kg A3 with 220hp, both having a power to weight ratio of 180hp/t
at 100mph you might be using 100hp just to keep the car moving, so in a 220hp A3 you've only got 120hp left to actually accellerate with, whereas the 270hp S3 will have 170hp "left", giving a "spare-power"-to-weight figure of 96 for the A3 and 113 for the S3... meaning at that point the S3 would be accellerating faster than the A3.
As the speed climbs the air resistance climbs rapidly, the amount left shrinks, and the more powerful car will begin to pull away.