How does the Destruction school fit into a "mage-assassin" build?

My main character started this way (a mage which used stealth in many occasions) and ended up as a full destruction mage, with very high stealth capabilities. After some levels (now 39 :-P ) I can tell that with decent Illusion level, stealth, invisibility and muffle it's a very sneaky character. As the previous poster mentioned the real issue is that destruction spells don't make finishing moves and are very loud.

Considering what I've written above, it's very good to sneak into a room full of enemies, conjure a good Draemora tank and cast a 100 Destruction Fire Storm or Blizzard... And I'm talking about 5 Falmers of equivalent level...all gone (alas the tank too). OTOH I'm playing a full assassin and in that case Destruction magic is pointless; perhaps only runes would be effective...

Hope this helps, Cheers

Well...this is interesting. Illusion is the trick to this build. I never bothered with things such as the points, as every character you make should have enchanting. 100% reduction for destruction and illusion are for my build. I don't grab impact, but I will grab Ice and Shock spells. Fire just has too much wow factor, whereas an icicle from the corner proves effective. The tricks being for 100% illusion reduction is that destruction spells, even with the illusion quiet casting, will still cause some semblance of an uproar. Which is where the 100% illusion reduction comes in. The use of Invisibility in a frequent fashion will yield great stealth results with no alarming of an opponent (to detected state, though clearly they may have some concerns about getting shivved out of nowhere.) All in all, there's not a need for dual casting in a build like this. I found that this build is just interesting and effective, and I personally find it more fun than say...the x30 dagger damage and overkill bow type stealth builds, because there's not exactly a simple way to upgrade your magic damage without enchants. Course, you could put points in mana and not build for 100% reduction in both schools, instead upping your damage output for your destruction spells. It's totally up to you. Personally, I like my simple stuffs. Also...I think people need to recall that Necklace, Ring, Helm, Armor are the four pieces you can enchant to 25% reduction. I'd like to hear of more build ideas, but so far I liked this one utilizing Invisibility best. Though it's definitely something that requires finesse.

The mod, Spell Sneak Attacks makes all Destruction projectile spells benefit from sneak attack multipliers, and items that modify sneak attacks, like the Dark Brotherhood's Shrouded Gloves.

It also adds a new "Silent casting" enchantment as an alternative to the Illusion perk (so you won't need to have a high Illusion skill just to get Silent Casting).

Destruction and illusion together with sneak can make a very interesting combo. Lay down runes near exits, sneak to the middle of the room while invisable, charge a master spell while invisable, and release, the enemies are weakened, start throwing fear and fury spells around to create more chaos, fleeing enemies are killed by runes and their enraged allies, and you slip away into the shadows... Slit the last guy's throat and you're done.

Personally, I like using the invisibility spell with my Destruction spells. For instance, sometimes I will apply invisibility to myself and charge a firestorm/blizzard. This way I can stealthily take a large chunk of health from single targets, or groups. Then you can just easily pick them off afterwards.