IIRC that perk affects all spells, so it could work in such a build...
You're quite right sir, I should've realised this being an Illusion Master

http://images.uesp.net/2/22/SR-perktree-Illusion.jpg
Quiet Casting: All spells you cast from any school of magic are silent to others (all shouts are also silent). Level 50 Illusion, required perc - Kindred Mage.
To level Illusion, take muffle, this will help your sneak greatly. Faveourite and bind it to a hotkey and use it as much as possible, even when walking in towns, before long your skill should be high enough. It's down to you where you sacrifice other perc picks though if this wasn't in your intended build.