The total damage for those few spells may be higher doing it that way, but it's the "Damage Per Second" overall that is important.
There is a GCD to weave something in for both, but a GCD in Astral Fire III with full MP is generally much more useful than a GCD when you are just going into Astral Ice MP regain phase.
Overall dps wise I doubt there is much difference between the 2 methods, but I'd go with the much more fluid method.