Damnations, I just realized I probably made a mistake in calculating the Aegis totals. I forgot that Wizard’s Vigil is at duration Sun, whereas the Communion in Core is at Momentary. This means that you have to deduct two magnitudes when calculating the effective level of the spell. That leaves us with a measly 15 effective levels for a level 25 Vigil. Since the summed-up levels of the Vigils need to equal twice the level of the spell being cast (50), we would need 7 magi casting Vigil (15 times 7=105) to cast the Aegis. That would leave at least four botch dice even after deducting three for Lares’ Careful Sorcerer. My assumption had been that we could do this with 4 magi (25 times 4=100), which would have meant 1 die.
Can you verify that I got this right, @silveroak ? It’s rather complicated, so I might still have something wrong.
If this is indeed how it is, then we will have to go with the level 30 Aegis. That means 4 magi casting vigil, and Lares can learn the Aegis without helpers. 30/4=7,5 , which means that there should be sufficient penetration.