You ask a very pertinent and good question. I wish you had made appropriate use of the Shift key while doing so.
One thing i would like to see is that once all things are considered, how do these specs change once we have to lose our 4p T7 bonus? Is it worth losing it? At what point is it worth losing it? If we don't use 4p t7 is the Glyph of Lifetap still the highest DPS glyph?