Aerodynamically the 68 is the obvious front runner. I don't know about 7 seconds but I'm sure there was definitively a difference. It would be more noticeable on a lower HP car. Take my old Mini for instance. When I lived in Italy I drove a 1991 Mini 1000. It had, you guessed it, a 1000cc engine and about 35hp. Shaped like a brick it would max out at 135kph and it took a while getting there. That was as fast as it would go, but the engine was not even close to red line. If I remember red line was at 5000 and at 135 it was running at about 3200. The same motor in a more aerodynamically conducive car, even with a little more weight would go faster. (After driving it for a couple of years and tuning on it and some custom paint I did get the max up to about 142kph)
The Mini
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