N62 is a great engine while it's running right. I wouldn't call it any better or worse than the M62 except that it develops more power/torque. They are both maintenance heavy motors...

You're right about the Bentley. If you want N62 information from a Bentley you will need to purchase the 7 series version to get it.

You will get 2 opinions about the 3.0i (m54) in an e53 here on the site. One (including me) is that they are gutless in an X5 that weighs 4700lbs and has Xdrive. We had an e83 X3 and the M54 was barely serviceable in that. The other camp says the 3.0i is perfectly adequate if paired with the 6 speed manual. I probably agree with that to a point... but 230hp still seems low for a vehicle this large.

The one thing everyone can agree on is that the m54 is most certainly the most reliable option for the e53 X5.

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2005 X5 4.4i Build 04/05 Maintenance/Build Log
Nav, Pano, Sport (Purchased 06/14 w/ 109,000 miles) (Sold 8/15 w/121,000 miles)

2006 X5 4.8is Build 11/05 Maintenance/Build Log
Nav, DSP, Pano, Running Boards, OEM Tow Hitch, Cold Weather Pckg (Purchased 08/15 w/ 90,500 miles)

2010 X5 35d Build 02/10
Nav, HiFi, 6 DVD, Sports Pckg, Cold Weather Pckg, HUD, CAS, Running Boards, Leather Dash, PDC, Pano (Purchased 03/17 w/ 136,120 miles)