Rich all I know is when you hit the ESP off switch the triangle in the center of the speedo lights up and you can do spins and doughnuts.
With the ESP on the car fights you and making it spin is almost impossible. I mean flooring it and cranking the wheel hard over at 20mph in 4-5in of slick snow. The car just wouldn't spin, slide yes but spin no. With the ESP off the rear will come around nicely. You can still feel the the traction controls acting up a bit but it gives you a lot of leeway and doesn't really interfear.
ESP makes a big difference with normal driving in the snow; you can turn it off and drive with a light foot. But on hills having it on helps a ton.
Just a side note: with ESP "off" these cars will do some awsome spins, lots of power.