+Spell damage vs +Chance to Crit Items

[bobbytk]

The thing i been wondering for a very long time now but never got into calculating

"increases damage and healing done by magical spells and effects by up to xx".

How much of the above do you need on a item so that that attribute is worth the same as:
"improves your chance to get a critical strike with spells by 1%"

This being on a frost mage with a 18 arcane / 33 frost talent spec.

From what i know to get the full effect of the by up to xx you need a spell with a 3 seconds or more cast time and instant cast spells count as 1 second cast spell(not sure about this but thats my knowledge:) )

I know this can be hard to calculate and take into account all spells so if ya take one spell take frostbolt as i cast that the most.

If anyone good at math can calculate this it be nice

[unothesmurf]

there is an item comparison program out there somewhere... someone's linked it somewhere on this site b4... srry, i forgot it...

[galzohar]

It not only depends on your spell and talents, it also depends on your current +damage and crit%. Basically it goes like this:
<damage>=(<frostbolt damage>+<item damage>*3/3.5)X(1+<total crit>)
Then u do the same calculation with your new item that you want to check out and see if it gives you more damage. If you want a more generalized calculation than u check how much damage additional 1% crit will give you and how much +damage will give the same gain.