ok with 20 stacks on soulstealer you have 375AP
Timebomb 330+412.5 = 742.5 damage.
Lets take into consideration that chars mainly have about 60MR in late game that gives about 40% reduction that leaves us with 445.5 bomb.

And this is assuming that you accualy have 20 stacks of soulstealer witch is quite hard to get with zilean beeing support char.

All i wanted to say in prev post that with only 2 AP items you wont go far in "killing".

sorry did math wrong timebomb deals 1.1 dmg/ap not 1 for 1.

I did the math and the mana regen/lvl are better at lvl 6. I'm gonna give them a try as soon as I get the IP up for it and I'll report how I do.

Dewo: you need to do your math right 156.25ap from Zhonyas ring, 25ap from the soulstealer (+10/stack), and 38.75 - 81.25 for elixirs of brilliance (gotta love that 25%) can get out about 550dmg timebombs (assuming lvl 1 and no stacks!)
with a double bomb thats 1100 aoe dmg that with a golem buff and ranked skills you can put out every 6.5 seconds.

Also Farming is the point, with a 19% exp advantage I'll hit lvl 9 while their still at 6 - 8, letting me bomb them at max skill lvl (usually no ap yet) for 330dmg, and keep it up without end (doubled for 660 every 18 seconds or so). then as I'm almost always finished with my mana and speed by then all futher gold is spent on AP, if the game goes really late sell the stone for rylais and the challice for Archangels (in that order) so you can keep up with the other dps. Generally games dont go this far however.

with 120 AP you wont go high damage with bombs.
You dont go for cdr also makes your spells way less spammable.

With this build you will just move fast, killing creeps and regenerating TONS of mana. Nothing more.

If you dont want to focus on damage zilean and play support than cap yourself at cdr so you can ulti speedup/slow and rewind way more often.

Atm i see this zilean as a fast running farm with ALOE of mana for enemy carry.

Shoulda went with my gut feeling of level 5... seals = .1 mana regen per level, meanwhile the base is .41 mana regen. So, at level 5 the mp5 per level is better. Btw, the website has rune planner, so you could have easily checked.

Does anyone know what lvl it is where you actualy break even on those. If it was as early as 6 I might have to consider it, any later though would be moot.

Well, you said you need mana early game, level 5/6 seems like early game to me, especially when you have your un godly amount of bonus XP, the mp5 per level runes will surpass the base mp5 runes in probably a few minutes.

I actually have used the ap but I find that since i dont go ap/lvl its not really that much. I prefer having a small chance t crit as zill has long range w his basic and a crit every now and then is nice. As for the shoes I am a speed freak and mobility is the most you can get, very good for jumping between lanes. as for magic pen I know but it was 6am when i wrote this, lol. Lastly mana regen/lvl just doesn't work for me, I need all the mana I can get early for being able to hold out. I just played a game where I solo'd against two and didnt die once, against blitz and coarky, and just kept them injured till my team came after finishing off their lanes and swept up, pushed all the way to base lvl 6. As for tear my build is pure economy and the only thing I like to get after my main build is strait ap + consumables, as if you dont get there quick you will become obsolete as they get more defense. and deathfire I just never remember, so i'll leave

Thanks for all the info though :-)

Just a few minor things.

1. Your seals, look into the mp5 per level runes. Its around level 5 or 6, that the mana regen from these runes surpasses that of the base mana regen runes.
2. Your magic pen runes are not a %, they are a base reduction. I read on here (cant remember where though) that armor pen and magic pen are taken into account like this...
(Their MR - Your magic pen) X (Percent magic pen)
*Note* When multiplying the percent, remember is .xx% when using a calc
3. You may want to take the 3 points out of the 2% crit and through it into the AP per level.
4. You may want to change boots to sorc for the extra magic pen or swiftness, I have never found mobility to be helpful unless im jungling for a while.
5. An item you may want to look into earlier on is the tear of the godess for the mana, and then you can turn it into the Archangel's staff. Another decent one is Deathfire grasp, once again, its created with an item that i like to get early on, kage's pick. These are just things you may want to try out during your game.
6. Nice Guide.

Wow, didn't know you could cancel opposing Zilean's bombs and warps. Good stuff to know. Also, excellent guide with good explanations of why you've specced the way you have. +1.