Originally Posted by Lazare

125mp5 = 25 mana/sec = 100 mana/4 sec.

Umm...that's just...bizarrely wrong. The GCD starts when you START casting. Since a talented GHeal is 2.5s, the GCD ends well before the spell does, so assuming zero latency, you can cast 1 GHeal in 2.5s (hence 200mp5). If we assume, oh, 200ms of lag then it might take 2.7s or so (or maybe 185 mp5). But it'll never take 4s; the GCD doesn't work that way.