earliest possibility to spec CI?

If it's any indication, I just switched to Low-life Solaris Lorica and have 4K ES at level 59, 3.5K ES with Geofri's Crest, and my gear is mostly self-found(Bought the Crest because it's awesome for casters, also bought the Solaris Lorica, because that's kind of necessary). So yeah, much easier to go straight into an ES build early on now. So you can pretty comfortably transition into a Low-life build at the end of Act 2 Merciless, and I imagine doing the same for CI would be even easier.