The recorded 0-60 time for the McLaren that seems to be adopted by most sites or mags or whatever, is about 3.1 seconds. There's no way an Enzo could touch that. That makes the McLaren ideal in this situation for a straightaway course. As amanichen revealed, the McLaren can handle better on corners, making it better in even a slalom.
Another point is obviously the weight-ratio. The McLaren is by far one of the lightest cars I've seen with such power in the car. This give the 600 bhp (the low) much more of an advantage on the <1000 kg, than the supposed 660 bhp for the 1350 kg Enzo.
Don't get me wrong, they are both beautiful cars, with nice power behind them, but the LM would be the sure winner.