I recently spoke to the guy at Milltek here in the UK who stated that after significant research it was proven that the optimum system for a cayman is: headers with cats (because the cayman engine likes back pressure) + cat-back with no cats. I guess when it comes to cars there is no such thing as one size fits all. He also stated that the header is the most important element to get right and is the place to start with any upgrades for the CS...