http://www.whnet.com/4x4/oil.html
Check the link--They really like the synthetics.
REASONS
Uniformity in lubricating properties, extreme temperature tolerance both hot and cold. Uniformity in molecule size, i.e., every drop is identical in physical make and chemical makeup, mineral oil is far from it. Synthetics will not break down under extreme heat, and they will lubricate in extreme cold. They will not "crush" under extreme pressure loads as well.
What that means is if you looked at a bearing race clearance filled with mineral oil and one with synthetic, the later would fill the void perfectly with no gaps, the former will not because the molecule size is variable. Ad VI improvers, as refiners do to achieve greater range in multi viscosity performance and you have odd shaped oil and plastic vs. uniform identical perfect molecules of lubricant. Cold performance is phenomenal, as MO 0W-40 will lubricate engine parts at -10°F as equally as well as at 185°.
Go for it, stick with the a 5K change cycle and see what goes, I think you'll be impressed in the long run.
PS, check with a good MB dealer, there is a SIL on oil that is really quite good, covers the Mobil 1 issue with regard to older engines.
MG