In my old RX8, I found the partially off stability control quite intrusive, mostly in rapid transitions. Better to lose time and cones learning how your car behaves than setting mediocre ESP-enabled times.
I havent run my 5.0 yet, but Im prepared for serious traction issues. Even though the RX had little power, it was very easy to break the rear end loose with too much throttle. It's always amazing how easy it is to overdrive a car in autocross.