Marauder - IW Arc - To Repent or Not? - Forum

Hey guys,
So I'm currently making an iron will arc caster with some block. Here is the tree I'm working towards:

http://bit.ly/1ZXEqKq

One unique I've been thinking about including is Repentance. It will require getting lots of
intelligence on gear to be able to use it, but seems to be an extra support gem for free, full stop. This will mean I can include something else in my 5L. (Thinking arc, echo, level 2 empower, penetration, then maybe faster casting for the final link?) Only thing I'd really be giving up is life and resists on rare gloves, so not too much of a sacrifice. I can afford to get a pair with a good roll as well.
My question is more about how much damage the extra 5th link will give me. Using an IW gem gives added spell damage with each level, and I'm not sure how to compare that with the damage I would get from faster casting or innervate. Plus I'll probably be able to stack more strength on gear if I don't have to worry about getting so much intelligence.

So worth it or not? How do I math this?

(Also any criticisms of my build are more than welcome)

Upon giving it a bit of thought, a level 20 IW gem gives 38% spell damage, plus lets say like 10 quality on the gem, so 43%. I'd have to get 120 extra intelligence on gear to use Repentance, so lets assume that I could get all 120 of that as extra strength, which gives another 24% damage from iron will.

So the iron will gem will give 67% extra spell damage over Repentance alone, as compared to a faster casting which gives 44% cast speed at a similar 10 quality, but also with a minus 5ish spell damage because of whatever roll I get on the Repentance. I'm sure the cast speed is a sizable damage increase over the spell damage, but how sizable? Worth the sacrifice in gear?

The only other factor to consider is sustaining. Not sure if reasonably leveled clarity will be able to keep me casting with all that extra cast speed, and the iron will gem doesnt have an added mana multiplier at all, so there's that going for it.

Hmmmm....

Final question - What is the best 5L for IW Arc using Repentance? Without?

Thanks for any tips!