The X5 traction control puts power to the wheels that have not lost traction. In the majority of winter weather it is all that is needed and can be improved significally with the right choice of tires. Generally, if that isn't enough you shouldn't be out there anyway.

Limited slip diffs are beneficial but I think mostly for racing when you want the traction control off and the TQ is enough to lose traction at any wheel or with two wheel drive. If you would rather not use the traction control feature for winter weather I would feel comfortable saying limited slip diffs will fairly similar to stock diffs.

The downside is you lose the effectiveness of traction control in cases where the vehicle is in a spin and the supplement to handling when pushing the wrapper when turning. And, Even if you can DIY, the cost of converting to limited slip diffs is very expensive based on a cost/benefit equation. You should not make the change to one diff if you ever activate traction control and to have the an effectiveness similar to the traction you should will need to do both anyway.

This is an opinion based on past experience with limited slip diffs in rear drive vehicles and the stock DCS system in the X5.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas