I decided to test out one of the Legendary Gems that dropped for me recently. These are new items added in a recent patch (2.1?) and can only be socketed into rings and amulets.
The one I decided to test was Taeguk
LinkGain 0.5% increased damage for 3 seconds after spending primary resource. This effect stacks up to 20 times.
Gain 0.5% increased Armor for every stack. (Requires Rank 25)
I tested it by removing an Imperial Topaz (+100 Intelligence) from my cold wizard.
Here are the results:
With Imperial Topaz: 519,898 damage
With Taeguk (0 charges): 512,970 damage
With Taeguk (3 charges): 520,665 damage
With Taeguk (20 charges): 564,268 damage
It's very easy to keep the stack at 20 during battle, especially with a wizard who's resources replenish so quickly.
Conclusion: Seems like this is going to work out just fine.
-420