EACH TIME PORSCHE sets out to design a new generation of its popular Cayenne SUV, it takes on the same challenge: making a car that feels more like a Porsche than a popular SUV. That is, ditching the rolling Barcalounger effect so common to these hulking vehicles in favor of the taut stability more common to cars like Porsche’s sports cars. And doing it without losing the comfort and utility that makes someone buy the Cayenne instead of the 911.