Flames kill quick if you pulse them rather than holding them down, because the "On Fire" status biffs stack quickly. Try alternating with it in each hand, and see how fast you can burn down certain NPCs.
For Impact, nothing beats Ice Storm. If you kite them into a line, you can stunlock an army, and they're even slowed when they're not getting hit by the waves of damage.
My favorites? "Wall" spells, not sure why they're called that, but 20 seconds of high DOT, and you don't have to hold them down, neither. All you really have to do is make sure they stay in the AoE, but backing a DP into a corner, you can burn him down quick with an inferno under him. Wall of Frost drains Stamina, so Dragons can't take back off, even Frosties, so it just takes longer to kill them. You got two hands, so you can hose them down with Lightning in the other, none of them are resistant to that. And finally, you can flame road Giants, and the like, by kiting them around, while casting WoF at your feet. I ran circles around Warlord Gathrik (To get that axe of Firey Souls to disenchant) and he followed me through the ring of fire until he burned up. Twice.
For anti-wizard, Thunderbolt. Don't dual cast, but charge up one, and then the other while letting loose the first to shatter their Ward. That stuns them anyway, so don't waste your Magicka on Impact. If the second ZOT! doesn't kill them, they won't have much to retaliate with, and will probably have to pull a dagger to charge you. Once you dial in the muscle memory to half-stack them, you can rapid fire alternating hands, with firebolts on up to Tbolts, all while running faster than they can in their heavy Armor, and weapons. Especially an Altmer, this is as close to Run&Gun as you can get in the game. (I originally started Half Stacking Magsecs in Perfect Dark.) By circle straffing with Fireball, you can pretty much carpet bomb them without hope of them catching up. Destruction is only weak if you don't know how to use it.
