Just keep in mind that Drifting-extreme slip angles is not the same as slightly rotating a car or sliding, F1 cars down to civics slide in and out of corners constantly, its just subtle, so to say driving a "line" is fastest could be taken different ways.
To answer the question, it depends on the corner, the amount of traction, going into, mid, and coming out of the corner, the amount of power you have etc as to what line or slip angle is the fastest. Typically a rear wheel drive car with decent power will want to "drift" when driven to the limits and its the drivers seat of the pants feel and ability to figure out if he or she is going forward or just burning rubber.
When the car starts moving around your at maybe 75 to 80 percent of its ability. That's when the fun starts