Button knocked 20 secs off the existing lap record in Hamilton's 2008 car not a great deal when you consider the time differential between saloon race cars/ GT and F1 on more conventional GP circuits
To be fair it's far from the smooth and grippy surface that an F1 car loves, and the only areas I'd expect a huge difference would be the few high speed corners and two long straights. Plus Lowndes was only a second off Button's time, so there would be more to come with an optimised set-up and bigger balls.