Nice write-up. Definitely going to give Sram's Expertise a run because of this article. I do agree with you that Kari's Expertise is the best threaten effect so far. The free drop really mitigates the tempo loss you would normally suffer from with other threaten effects.
I used to write cube articles on StarCityGames, now for GatheringMagic and podcast about cube (w/Antknee42.)
450 Unpowered Cube Cobra