The cast time is not Instant (could you imagine if it was?) It takes approximately 11-12 seconds to complete the cast. Figured it out so I could stick /wait 12 /equip main "Earth staff" into my macro afterwards, helps with not taking as much dmg if you pull hate from the cast.
Yup, this is definately the most damaging spell we get. Makes a very cool sound that almost makes you feel like shivering. Makes you feel like someone is scraping a chalkboard. Insane damage for sure.
Personal best of 1859 DMG on a magic burst in Ro'Maeve on Darksteel Golem. Dual thunder weather on darksday with thunder staff. Should be over 2000 if on lightningsday w/ dual weather, and all 3 added effects kick in.