[thstone]

The easy answer is the 996 GT-3 front adjustable front (from Porsche or Tarett) and the Tarett rear adjustable sway bars.

On the softest settings they will be 50% stiffer in front and 30% stiffer in rear as compared to the stock S model suspension. The good thing is that they can be adjusted as you improve your suspension components (coilovers + springs), improve tires (NT-01), and improve as a driver.

As others have noted, the suspension has to be viewed as a total package - everything works together. Optimizing one characteristic (like roll stiffness or damping) won't yield huge benefits if other characteristics are still lacking (like camber).

Thus, the biggest bang for the buck is camber. Without enough camber, it kind of won't matter what else you do. Camber is intimately related to tire choice and driving skill. The stickier the tire and the better the driver, the more camber. After camber, then the car needs stiffer springs and improved damping. Then fine tune the roll stiffness.