Dirty bird you are talking out of a book and that is a USA book to boot not metric when you say the thread depth should equal the bolt diameter is not the rule for metric bolts due to the finer more shallow threads. I have seen many pull tests over the years and that theory of the bolt diameter is nothing but reading material on smaller fasteners no mater what thread they have.
As far as a muffler locktite go's I use the blue and so far have had good luck with it, for years I never used anything until I had one come loose on me.
You claim the red does not have the heat range needed for a muffler but yet it sometimes takes a torch to get it loose. I think the 425 degree rating is well under what it really is.