40/21 to 10/48/3 - When to Switch?Follow

Just wondering, is there a 'magic' number that my spell damage/spell crit needs to be at [before counting in mind mastery and all that jazz] where the 10/48/3 build surpasses the 40/21 build in terms of damage?

Currently, my mage has roughly 800+ Damage [not counting, of course, mind mastery] and about 22% chance to crit. [Once again without the talent that increases crit chance/spell damage] Her hit is probably a bit low, I'm working on getting that sexy belt from badge turn-ins and the dagger from Zul'Aman.

So, my question is, when do you switch to 10/49/3?