The Le Mans Classic vid is very good, obviously very wet and slippery with lots of wheelspin. Note the non-functioning speedo, it would have been interesting to see what speeds the guy was reaching.
The Cobra 289 was doing a pretty good job of keeping up. On the Mulsanne he definitely dropped back. I think the aerodynamics on those (even with the funny top) was such that they didn't go much past 155-160 so I'm guessing the GT40's were topping out somewhere well past that.
I was impressed with the Cobras ability to get power to ground out of slower corners, but would suggest that there is a lot of difference in tires/compounds used from car to car at this event, 108 did not impress so much, throttle/clutch coordination at shift points and trailing throttle/engine braking rather than using brakes could lead to problems in an actual 24 hr stint