Per square, Shocking SCs beat Shocking LCs. But based on ilvl rarity, Shocking LCs are really supposed to go head-to-head with Arcing SCs, which they will beat per square.
P(Skiller, 40 < Life) = P(Prefix and Suffix)*P(Suffix = "+(41-45) to Life")*P(Prefix in SkillersYouLike)
= (1/4)*(4/100)*(x/244)
where SkillersYouLike are the skillers you want and x is their number. The result becomes more depressing the pickier you are. The chance if you like all skillers is around 1 in 1162.
How early? Pre 1.10 Ravenclaw mows down most opponents in normal (shooting slvl 30 Exploding Arrows which deal 259-301 damage). At some point, speed (and more importantly pierce) outweighs this damage. Ravenclaw of course still applies the Enchant damage on top of the massive Exploding Arrow damage.
Regardless, I would personally go for Doomslinger Demon Machine (I assume you meant this), as attack speed is important and the Enchant damage is more than enough. It also has pierce.