First: Circles of magic are the spell lists for variant Mage types (including the original class, now called the Magician). As such, all Circles of magic use Reasoning as their second spellcasting stat. If you have two Mage professions with the same spell on both lists, the choice would be between Reasoning and Reasoning (i.e.: no distinction).
That said, I've had GMs who went several different directions on this... including one who took 3 different positions, depending on the situation and/or the character's backstory. I'd say ask your GM.
Then again, if you're the GM, I would urge leniency. I kind of imagine that nearly all the ranks to cast a spell are universal among all the different versions for all professions, with only the last rank differentiating them. Above the minimum ranks, any improvements are from personal understanding and practice. Ergo, since the last rank is what makes a difference between a harper spell and a mage spell (the 7th rank of changing ways, for example), it's reasonable to assume that final rank is what determines what stat is used to cast the spell. As soon as you've bought at least one rank of a spell in a new profession, what you're learning is their version of that last rank, which would include the specifics necessary to base your spell on Reasoning, Insight, or Presence.
