1.2.0.3 UPDATE!
Mr. @banana_peel had the idea to bump casting speed on this one by using Dread Skull in medal and a Gargoyle Girdle with casting speed affix (and also using Will of the Fallen Kings rune that procs Targo better). I tested it and after few minor tweaks decided to update the spec: it’s indeed a little better overall. The trade off is a bit of flat retaliation damage and a bit more expensive gear (you can still use blue belt of course), but it’s definitely worth it in the end. Plus there are two affixes between belt and medal that work: Light Bringer’s and of Gildam Arcanum which makes it a bit more flexible (both affixes are among the most popular rare affixes in items pools and have around 2.2% to spawn, as corroborated by drop rates mathematician @modal).
Here is a snippet of loot tables for Gargoyle Girdle look, for example:
Find the updated grimtools in the op. Here are the videos with build’s current performance: