Let's go over my units:
Teclis - Between Banner of Sorcery and the Moonstaff of Lileath, Teclis can generate an average of 11/12 Power Dice for himself at the beginning of every turn. What you do with this is strictly up to you. For me, the general options are: Throw a giant spell like Purple Sun of Xereus out, full blown with 6-7 dice because even if you roll double 6s, you ignore your first miscast. Once that thing hits the table, it will cause absolute havoc for your opponent. You can also choose to cast more cautiously, throwing 3 dice at medium cost spells and up to 4-5 for high cost ones. With an average roll, you should be able to IF these spells without dropping your concentration or anything else too drastic. Just keep in mind you always have that Scroll of Hoeth in your inventory and use it when it matters. Also keep in mind that just because Teclis is awesome at casting, doesn't mean you have to sit in the unit and cast without fear. He is still the most fragile mage in the game with T2 and 3W with no saves of any kind. Don't be afraid to run him out of the unit and cast some support spells because keeping him alive means absolutely everything if your army is focused on him.
Archmage [Book of Ashur or Hoeth] - For 330 points, the Lv.4 with Book of Ashur is now one of the best buys in the book. The fact that the mage gets +6 to dispel before any dice are thrown is just gigantic. That, combined with the fact that he also gets +5 to cast means that most low-medium spells are cast much easier. Since you can now switch out spells for anything that rolls a double when you're randoming spells, getting the spells you need is much more reliable for a Lv.4. The Book of Hoeth on the Archmage is also a pretty solid buy. Having IF on any doubles as long as you reach the casting value lets you break through magical defenses if you throw enough dice at it. Just be mindful of what spells you're trying to cast and always cast the big ones first if you can. Casting a lower level spell and having the chance to lose concentration and not being able to cast anything else is bad.