from the perspective of my FH crits doing nearly the normal amount of a GH an then being able to do just under 3 FHs to every GH then i cannot see GH becoming useful compared to FH,
FH raid crit- around 7500+ (with weakoned soul + other talents FH crit rate is fairly high, without working it out i imagine around 50% ?? anyone able to confirm?)(normal hitting just under 5k)
so in 3 seconds you get between 15k and 22.5k + divine aegis......
GH, 2.5s for the cast... normal being 9k heal, crit- 15k.
so 1/5 of the sp (for the extra 0.5s to make the calculation worth while = ) 1.8k normal, 3k for the crit,
so 10.8k- 18k for the GH + divine aegis.........
thats with standard gemming, not for haste, gem for haste, lose the spell power, sure you can do more GH but they are less powerful, and you might as well go holy because disc has the haste values there to make FH effective for the spec.