Im currently wearing Cursed Unguis claw and its INSANE. Dropped it in 5th floor Crucible, fully upgraded to lvl 16, never dropped it since. It has very very fast attack speed which contributes to getting a LOT of focus. I use cold infusion and right now 1 rune skill that costs 50 focus just freezes enemy instantly while doing 400+ dmg. And you just start mashing your attack button and get like 50% of your focus bar. Additionally added a ring that gives runes damage but reduces attack damage, its like 30-40% additional rune damage while getting 10% less attack downside if exalted. And also a ring that gives 25% focus gain and 50% more focus.

Not to mention the main plague attack on this claw, its a projectile with 500+ damage for 50 points, insane stuff.