X5 ranked in the bottom third of the segment by JD Power in 2015, which is about all you have data-wise. Anecdotal remarks by individual owners are not that useful. My '15 50i looks and drives like a brand new vehicle and I love it. But I would be nervous not to be under an extended service contract to cover major problems like transmission, motor, turbos, etc.
http://www.jdpower.com/cars/study/20...emium-SUV/1133