Go with all of the gear and spec maybe 30-40 dex. If I figured it right, your cast time should be that of around 145-150 DEX, or similar to it. It's close enough to IC where any cast is pretty much near instant, but if you're going up against a High DpS class it may or may not proc.
My HWiz friend did this awhile back, she achieved near IC and we still raped anything we could (it was mainly Niff though). It's not a bad strategy for cast reduction gears.. I'd say the whole of em might cost you around 35-45m instead of the kahos themselves being 70+m to BEGIN with.