Quick of the top of my head math.
I'm going to use a crit value of 33%, just cause its a nice number. (Raid buffed shadowpriests should be well over this value).
(I am ignoring crit bonuses to specific spells from talents and tier sets.)
I'm not going to get into the relative scaleing of sp vs crit, so i'm just going to treat the damage of a spell as a constant.
Total Damage=(Spell Damage)*(1+Crit%*CSD)
Total Damage=(Spell Damage)*(1+.33*1.03)
Total Damage=(Spell Damage)*1.34
Without CSD
Total Damge=(Spell Damage)*1.33
Total Damage with CSD - Total Damage Without CSD
= (Spell Damage) * 1.34 - (Spell Damage) * 1.33
= (Spell Damage)*(1.34-1.33)
= (Spell Damage)*(.01)
This means that the CSD adds roughly 1% to our damage, and as spell power and crit go up, so do the value of the CSD.
Additionally, as of now we have no mana issues, and gain runspeed from our boots.
The only useful benefit we could get from another meta would be 2% less threat.
IMO ~1% extra damage is > 2% threat, especially as I run with good tanks.
Once we hit level 85, with its corresponding lower values of crit, then it might be useful to reevaluate the CSD, but for now, it still reigns supreme.
*I over simplified the damage equations, so my numbers are very approximate.*
*Edits were to try and get it to display halfway decently.
*Last Edit fixed a *Very* stupid math mistake. Numbers should be correct right now.