Well, I am a mechanical engineer (registered P.Eng.), but let's leave that aside since the following is based on judgement, not calculations.

I would go with the extension/drop limits of the standard E70 hitch, which you have, instead of the E53 version. That probably gives you a reasonably level trailer in any case.

I don't think that the engineers tested for any of your scenarios; I think that they calculated normal static loads (no WD hitch) and applied typical safety factors, and then left it at that. You are going an order of magnitude deeper into the calculation than the poor sap who wrote the manual, IMO.

Now, here is the key point. I haven't designed or analyzed WD hitches, But intuitively, doesn't the weight distributing feature naturally counteract the bending moment of the static load on the hitch ball (since it reduces the weight on the rear axle, and doesn't increase it)? Think about it; the static load pushes the rear of the X5 down, and the WD hitch lifts it. Opposite effects. They tend to offset each other, not aggregate. There is a stress point at the hitch ball where the WD hitch has the ball and the WD levers attached, but that is part of the WD feature. The 2" square receiver and the part attached to the vehicle sees the net effect, it seems to me.

So, given all of the above, and what I know about the sturdiness of the BMW hitch, I would just do it. But again, that is just me. See if you agree with the above, though.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
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2003 X5 3.0 Steptronic, Premium, Titanium Silver
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