Just had a quick go, managed a 1:19.753. Driving that SLS was a bit of a shock because the last couple of days I've been driving nothing but racing cars which have lots of tyre and aero grip and the Merc has neither.
Also, the 'invalid lap' restrictions seem tighter, I kept getting caught out by going off line (to the right of the darker racing line on the tarmac) too much on the way into Chicago and ending up with a red time. I always use that line, because I can get the car straight quicker and can therefore be more stable under braking, and it never normally gives me a penalty.