Oh boy....here we go. Lubricants, like cameras, stereos, shoes, and everything else, tend to bring out the passion in people. You cannot 'win' an argument over lubricant selection. My choices have evolved using personal experience as well as selected recommendations of people I think are smarter than me.
As far as Red Line, you will pay a major premium for the privelege. Sure, if you have super-duty high stress special application, Red Line probably makes sense. But it amazes me how people will drive a car for 15 years and 150,000 miles and want to change to the best lube they can afford. It just doesn't pay out. All of the lubes that conform to the manufacturer specs will work just fine. Fact is, I've never heard of a diff that failed due to lubrication brand - from any of my friends or even discussed on many car forums. Also, Red Line is not that easy to find for many people. Why bother?
IMHO.....Red Line products are not needed for the vast majority of us everyday drivers and off-the-shelf stuff works just great (donning fire retardent sprayed asbestos underwear).