Here's my 2 cents on it...
Shift 6 spell declared, well within the range of his conviction (+4) + focus item(s) to control and cast.
The roll nets him +2 for a total of +8
So Far One point of mental stress.
I'd really like to know what the character's Discipline and focus items are so I can dig down into the math. If the conviction is +4, I'm assuming at this point that his Discipline is also +4 with appropriate focuses to compensate for the 6 shift spell. So, he is now at +8 to hit with a weapon 6.
He takes 3 more mental stress voluntarily then takes a Mild Consequence to pay off 2 of those, thus another +3
total is now +11
With 2 mental Stress
.
Ok, I know you can do this voluntarily in Thaumaturgy to help power spells, and I know you can do this to take Backlash to actually cast the spell assuming your Discipline roll does not equal the power you are pushing, but I am not 100% sure you can voluntarily take damage like that to cast higher powered Evocations. I'm going to have to read back over the rules on this.
Tagged at least 4 separate aspects; two or so on himself and two or so others from other are tags available. So that's +8 more. Total is now +19
Costing 4 Fate Points really make this powerful. You mentioned only two or so were his own. Were these other Aspects found out about the enemy via Assessment?
Used 4 points of Sponsor Magic for another +8. Total is now 27
What Aspects was he Invoking? So, for Fate Points you can use them a few different ways. Without an Aspect to invoke, it only counts as a +1. If you have an appropriate Aspect to invoke, then it's +2. So far from what you've said, he's either invoked all 8 of his Aspects or my Math is really off.
Dropped 4 fate Points for another +8. Total is now 35!
By my count he's out of Aspects to invoke and Aspects can only be invoked once per roll, so at most this would only be +4 (using the rules governing the use of Fate Points above).That is unless some of the Aspects he's already used are really Consequences the Monster already took or Aspects of the Monster that have been found out through Assessment.
2 Wool-gathering Maneuvers for the additional +4
So the total ended up at 39.
By my count it is as follows (I am not counting the taking voluntary damage to power up the evo, as I'm still not sure that's kosher.)
+32 to hit with a weapon 6. Depending on what the monster rolls to dodge, that only takes off 8 (assuming his Athletics is 4). So it's a +24 to hit with a weapon 6 if the monster rolls 4f to dodge, giving a potential for a 30 stress hit.
Now, the character has depleted a MASSIVE quantity of Fate Points in addition to incurring quite a bit of sponsor debt. As Warpmind stated though, according to the simplified description of the rules, you determine power and you roll to hit. Although with other skills, you could keep invoking Aspects to gain extra to hit if you *REAALLY* want to make it count.
Also, a lot of this assumes ALL of his Aspects can somehow be Invoked.