Flame cloak seems to do a lot more damage than stated. I'm on master level 59, meaning the guards will be at the highest level, and flame cloak will kill them in ~20 seconds. The frost and shock version do barely any damage, but the added damage of the fire does a decent level of damage.

You can cast flame cloak, then go invisible/become ethereal and just sit next to your enemy until they die. It's cheap I know, but it's just something I found ha. I assume the dark elf power will do even more damage, also the unique effect from the ebony mail (poison damage per second) will wither them down even quicker.

Dual casting flame cloak doesn't seem to do anything, damage or duration doesn't change.

Just thought I'd share ha

Also the cloak spells seem to get rid of any summons you have, not sure why.

Are they Conjuration spells?

No they're adept level destruction spells.