I will go out on a limb on this subject but this is my experience.

In my 35 years of packing Lobro CV joints the best thing I have found for
extending their life is to use an excellent brand of synthetic
extreme-pressure CV joint grease instead of a conventional EP grease.  My
experience is with the semi-synthetic Valvoline DuraBlend EP grease but in
one example I used this with Vanagon CV joints that had significant pitting
and after repacking with DuraBlend and driving an additional 50K miles with
a 165 hp Subaru engine the wear looked exactly like it did when they were
installed.  The joints were worn initially on the same vehicle with an I-4
conversion while packed with conventional EP grease.

http://www.valvoline.com/pages/products/product_detail.asp?product=3

I can't speak for other synthetic greases but Valvoline DuraBlend works
great for me.

Please note that I have always used molybdenum fortified CV joint grease to
pack CV joints.

Before I started using DuraBlend I tried reversing the direction of the load
(by swapping axles side for side) with the expected results:  The joints
developed wear spots on different places in the same amount of time.

I have no connection with Valvoline in any way but I do like their CV
semi-synthetic grease.

Ed McLean