My wife has owned both a 5 speed and a 6 speed X5's.

The 5 speed was a '01 that was totaled when a lady pulled directly into my wife's lane in a snowstorm.

The 6 speed was the it's replacement and has since been sold to ChiefRider here on the forum.

We owned the 2001 for about two or three years, the 2004 we had for 8 years.

The 2001 gave us a bit more trouble than the 2004. The 2004 was a great truck very dependable and reliable.

The 6 speed lowers the RPM's on the highway a few hundred RPM but it's not nearly as much as one might expect. Both have short 1st gears.

We never had any issues drive train wise with either vehicle. Both are sound transmissions. I do believe the haldshafts and transfer case was changed/up-rated in '04 with the change to the 6 speed.

I would shop by quality of vehicle and would not hesitate to buy a 5 speed with a good service history. The 6 speed is nice and you get a few years newer vehicle but, they are harder to find than the 5 speed.