Cary, there are LOTS of things to consider for either 6 or 8.
both offer advantages/problems.
Honestly this has been beat to death over many threads, so just search for "problems" or read the "How To" section at the top of the website to see what repairs are documented so you know what to look for.

so many to talk about.
PS: just as a few topics, look for Panoramic moon roof, air ride suspension, ride height dropping, bluetooth troubles, engine problems, transmission issues, torque converter issues, door carriers... lots of issues with both designs, but lots of fixes.

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I swear, my cars are like a girlfriend.
Sometimes its a rough ride, sometimes its smooth motorin'.
Sometimes she doesnt like how i treat her and sometimes i dont like how she behaves.
BUT at the end of the day, she loves it when I am inside her.

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'91 850i
'05 X5 4.4i
'09 Clubman S