I believe you misunderstood. An re5 is a slam spec bag. There is no way to keep a stock spring and use a bag to lower thid vehicle..the re5 replaces the stock spring along with the cups jason would make for you. Having had several bagged vehicles I would question that the ride is the same as factory. It would only be as good when the psi in the bag gives you an equal spring rate to the stock spring rate, and even then I would doubt the xf would handle as well from my experience but it may be comparable.