I thought I would close the loop on this thread and state that after much analysis and all things considered I purchased Koni FSD's with Rogue Engineering RSM's and I could not be happier after driivng for a couple of months. The ride is stiff yet comfortable on the interstate. My E46 is tight and drives like it did on day one.
2014 BMW X-5 xDrive 35i F-15
2006 BMW X-5, 4.4i N62 engine E53