Go skeleton for beefiness, pick up impending doom for single targets. Probably other stuff you can do, too, but if you're looking for a single-enemy fuck-you-too-sir, there's not much in the game better than impending doom. That talent is a goddamn menace.
I mean, they've got other stuff they can do (and once you get things rolling, especially with fire, everything just melts because you've probably got 100% respen and so much +fire damage faerosi cringe in horror), but I just spent like four or five hundred turns playing smack and away with a bastard with impending doom.
I also just realized ID's a goddamn necromancer talent, not archmage. Right. Yeah, conceptually they're more about the AoE layering, so, like, do that. Drop inferno and freezing vapors and whatever BS the arcane trees are crapping all over stuff with nowadays and then teleport away and let crap melt. Can't teleport, pop bone armour and laugh 'cause you just shat out a 1.5k hp shield at like level twenty or some crap or throw up stone wall and go nyah nyah nyah. Hit the frakkers with mud slide or tidal wave or whatev' and then PD yourself (or movement infusion -- if you're not undead, you can use those) to the edge of their range and let them wade through your fields of death all over again. Or PD them to the other end, either way. Basically, archmagi have a crapload of options -- specialization isn't necessarily a bad thing, but even a specialist mage wants all that tasty-as-hell utility. Get it, use it, yeah.
Regarding the orc patrols... it might be worth throwing an idea post up on the forums suggesting rares get squelched in those. They were quite doable for however many betas there were before the breeding pits were implemented, but I do imagine the inclusion of rares has been a nasty stealth buff. Or play with the opt-in advn parties addon, which I think covers orc patrols, too. Well, or code up an addon with an alternative

In other news, I've been reminded that yeek berserkers kinda' rock the house. I'd forgotten about that, and have noticed a neat synergy where the global boost mostly makes up for the penalty from precise strikes, which means I can go str/dex/con and still have fairly ludicrous crit rate (59% at level 24, whee). Anyway, yeah, enjoying this so far. Fair bit flimsier than your normal 'zerker, of course, but that still means I've got like 700 HP and a hefty chunk of HP regen.