Dan--Highly dependent on the car's weight, mechanical braking ability, speed, the track and the driver (as well as how fresh you keep the stuff).

You want the best fluids, but stuff that is a known quality.

You will get lots of opinions, but unless you have experienced fluid boil, I would say that you are OK with what you have.

I personally like a good DOT 4 and use Genuine Mercedes Benz Brake Fluid, but I am pretty sure its composition is ATE Gold.