I just ended up trading my 2008 X5 4.8i for a 2009 GL550. We have a 15 month old, and are getting ready to have another. Just not enough room for all the little kid stuff. When we went on road trips in the X5, barely had enough room for mine and my wife's things plus the baby's. Couldn't take golf clubs or anything extra.

Comparing the two, the X5 is the better handling vehicle. The MB, however, is extremely nice. Much better back up camera, sound system, overall ride quality (not handling), acceleration and transmission. Handling is very good for such a large SUV, however, it is NOT a BMW. Our X5 stickered at almost 73k. The GL was almost 87k. Costs me about 300 more/month.

My wife loves it. It is her vehicle. Very agressive styling and look. Love the 21 inch wheels/tires, and are much better in snow than the X5's 20's.

When our 2 kids are about 3 or older, then we will go back to the BMW. Until then, we need something a little bigger. The M5 is still my DD.