Mage/Priest spec through Northrend? (Prefer single target)

Ive never been the type to like to aggro entire areas and aoe. Ill do that occasionally, in any of my dualbox mixings but for the most part I like to burst targets down. Atm my current is a full frost mage level 65 and a lolsmite holy Priest level 64 (mage is a bit ahead):
http://www.wowarmory.com/character-s...alyon&n=Vindle (Missing BoA gear and new chest)
http://www.wowarmory.com/character-s...n&n=Holydemise (Missing BoA Shoulders)

I stopped playing both because I got really really bored. It was basically Frostbolt/Smite spam twice and dead. I know a little about Mage's arcane but nothing about fire (same wtih Priest's shadow). I was thinking about trying Arcane/Disc but id lose the lolsmite but gain penance (never tried that spell before). I dont think shadow would be best cause I still like to keep bubbles and heal my mage.

Ive gotten other dualbox sets to 70, but want this set to actual go past 70 and do northrend as a dualbox (ive done solo twice so nothing but the dualbox is gonna be new). Any input would be great, I dont think theres anything wrong with the combo I think I wanna find a change of pace that I dunno what other combo spec would be good for questing. Thanks!