Wow. I had the math on that ALL wrong.
So if she changed her Conviction to Great, that means her evocation has a base of 4, +1 for Focus Item. This drops the Overcast to 3, for a total of 4 stress. Since her Conviction was boosted, she now has 4 Mental stress, so she could take a minor consequence to reduce it to 2.
correct.
I'm not following how Rote changes the amount of stress you're talking about. Why would it be different as a rote? The power generated by the spell (8 shifts) is static, yes?
New to the system, trying to figure out how all this works in practice as opposed to theory.
It's not the base stress that changes, it's the result of the control roll that is fixed when using a rote.
The Rote fixes your control roll at +0, meaning that you automatically control any spell that can be controled with you discipline skill value alone.
In your case (Good (+3) discipline) that would mean that up to a +3 power spell could be controled without trouble. anything more that that would cause backlash or fallout.
With the power 8 spell, this would result in 5 shifts of fallout or backlash. Fallout is basically damage to everone and everything around you, and it reduces the effective power of the spell, so it's no good to us. Backlash is damage to the caster i.e. stress, but it leaves the spell intact, so that all of the powers is actually in effect. So you'd take another 5 points of stress in addition to the 6 points already taken.
To avoid those 5 shifts of b&f you can invoke 3 aspects to push your control roll to +9, controlling the spell without damage.
Fallout and backlash can happen to you when you use the spell normaly as well. You summon 8 shifts of power (with +3 conv. thats 6 stress regardless of it being a rote or not) then you roll your discipline to control it. Resulsts ranging from -4 to +4.
best case you roll +4 and have now arrived at +7 for the control roll. Meaning you still need to invoke an aspect to get to 8, or take the remaining shift as backlash or fallout.
Worst case is -4 making your control roll a -1, meaning you have to take all 8 shifts as backlash or fallout, or invoke 5 aspects to get to a control roll of 9 (8 or higher)to control the spell.