Switched from my '06 750i to a loaded '08 4.8 X5 primarily to carry more loads (dogs and stuff) to our second home. We now have 2 4.8 X5s - an '07 and '08, both loaded. Great performance, not as smooth as the 750, a bit more choppy but still great for a long journey. Engine noise more noticeable, but this is an SUV and not a sedan. The big tires on the performance package have plenty of grip, huge cross section, work well in the rain (unlike the MB GL550), although there's some tire noise. We switch to snow tires in the winter and the noise disappears. Interior and equipment are great, driver sits higher than the 750 but the car is just as chuckable, with no body roll.
BMW comfort and performance! I've used the iDrive for years on many BMWs, this latest generation is different, takes a long road trip to work out all the features. Audio interface has finally come together, choice of radio (HD and satellite), CD, iPod, etc.
Rear camera is a disaster, OK in normal daylight, but washes out at night. BMW needs to take the one from our Chevy Avalanche which provides crisp, clear pictures night and day. Spoils an otherwise perfect car.