You'll probably know a good portion of this, so I hope it doesn't come across as too patronizing :P
Insta-kills still work; it's just that fort saves are very high. Like so high that DC 55 or 56 against some EE mobs' fort saves isn't reliable (without debuffing first). Orange and Red names are also flat-out immune to instakills on EH and EE (so just go to town neg levelling oranges - web or dance or discoball or hold as optional, and DoT reds).
Also, some mobs have high reflex saves too, so web doesn't always do the job (but coupled with solid fog it's a reliable and marginally cheaper option than discoball + mindfog where you can get away with it).
My personal take on will saves is that discoball lasts longer than mass hold, and you can run them back through it if they save so yay. Mindfog also effectively adds another persistent 'must-make it or be CCed' save if you put it in the discoball.
You've probably seen Faent's giant Magister Le Suck thread. It's worth the read as it canvasses both sides of the magister v draconic debate reasonably well - some posts even consider Archmages!
I'm firmly in the Draconic camp, especially for AM's given we can't spam PM SLAs in the hope of getting the fort debuff proc. That said, I think there's a unique opportunity for AM's taking SF: Evocation to be able to spam Magic Missiles to an even greater extent than PMs in order to proc null magic strikes, so Magister's less awful for Archmages in that regard.
I'm doing:
http://forums.ddo.com/showthread.php?t=398520 - which is a mammoth thread I don't expect anyone to read the entirety of, but suffice to say, I think in both Magister and Draconic you want to max INT (and therefore DCs). I went Illusion Fleshie AM too, so it's not super relevant, but I give a full breakdown of what I take in each of the EDs.