I'm 6'5, and one of the main reasons I bought the X5 was because of the leg and shoulder room. When I'm running out to starbucks in the morning before a shower, my hair can be scraping against the liner, so I couldn't see 6'9 without sticking your head out the sunroof .

Just from test driving and comparing though, the MB GL450 has more headroom than the X5. I know that doesn't really help you, but just passing the tidbit along.