Storm Atronarchs are tough because everytime you hit them you lose heath this also applys to Clanfears so in order to get around it I suggest getting your reflect damage up with ring of iron fist and neckless of swords this makes it alot easier to beat them.

Any other ideas are much appreciated

My character normally softens them with a spell that does three things: Makes them forget you just hit them with a spell, weakens them to poison (busts their immunity) and prepares their soul for capture. Then she shoots them with a poisoned arrow and waits for Azura's Star to announce their death. She wasn't aware that they were dangerous.

The problem is that storm atronachs and clanfears both reflect damage. Storm Atronachs reflect 15% and Clanfears 20%. I don't think damage can be reflected twice, as in you reflecting the damage that they reflected back at you, but stacking reflect damage would definitely help since it would reflect their own attacks. The trick is magic and arrows. Reflect damage does not apply to your bow and arrow, so using one against these enemies takes care of that annoyance. Additionally, neither creature is resistant to all magic. Using any non-shock magic will work great on a Storm Atronach, and conversely using shock magic will be extra effective against Clanfears (they have a 20% weakness). More on them http://www.uesp.net/wiki/Oblivion:Daedra

Using shock works great, too. You just have to use a custom spell with 100% weakness to shock and 100% weakness to magic before using your shock spell.

I try to avoid melee on Clannfears and Atronachs because of the damage reflection.

For a Storm Atronach a very skilled mage could handle them without too much trouble by using some weakness to frost, weakness to magic and frost spells.

Why don't you simply drop a bomb on them?