Tom, as was said, vented rotors are of two sizes. Stock thickness of 0.810" x 11.3" OD and the wide-body 1.25" thick x 11.5" OD. The thicker ones are similar to what the Gr-4/GT-4 factory cars used with some success at LeMans. Pro racing heat loads are such that brakes need more thermal mass to stabilize at a temperature below that which will cook pds and boil fluid inside the calipers. Which, by the way must also be replaced when using thick rotors.
The thinner ones (with stock calipers) are for street use and light competition- like autocross or a few laps of amateur open track days. Any prolonged use of thinner rotors will overheat them, just like the stock solid ones. But the thin vented ones do reduce sprung weight and thus aids day-to-day handling.
Bottom line: if you can lock up your brakes now, you don't need bigger brakes, you need more tire. All bigger brakes will do is make it easier to lock them up.
If you cannot lock your brakes, then your car will benefit from better brakes- perhaps even aftermarket assemblies.