My opinion differs significantly from deutsch's, but I want to throw it in as well. In my opinion, the X5 rides hard, regardless of model or Sport Package or not. On the bright side, it offers great handling for a 4,900-pound SUV. Your choice ultimately depends on whether you want more sport or more luxury. If you opt for the Sport Package, you will get a stiffer ride but better handling in the turns, along with bigger and sportier wheels, the sport steering wheel, and the sport seats. If your main focus is comfort, do not go for the Sport Package as the X5 will offer a more comfortable ride while still providing solid handling in turns as a BMW is always a BMW.
deutsch mentioned an important part of the X5 4.4i's Sport Package. If you opt for that, you get 18" all-season tires all around, but you can additionally opt for 19" wheels ($1,000 option AFTER you get Sport Package)....the 19's are summer performance tires which will not do well in cold weather, especially ice and snow.
I do not know what Denver is like, but we visit Vail every year for skiing trips. As I prefer performance over comfort, and knowing that you guys have some nice 75mph smooth highways that run through the mountains (nice curves!), I would opt for the Sport Package and enjoy the drive. [driving2]
