I have three questions relating to what stands to improve your chances of saving against a song (and subsequently what a bard can do to overcome it) but to fully understand what you can do against a bard you need to understand what is working for the bard.

The first part is the instrument.

The second part is the repertoire and the song being sung in that repertoire.

The last part is the charisma.

I understand charisma stat is a base boost to songs. Is this a boost to the song level itself (and is the song level based on the instrument's suitability to repertoire) or does it have a more indirect affect? Can this affect be compared to the affect mages INT has on spells? AP's? Or is it a different mechanic entirely?

Is singing canticle of the gods and eyeing the tick timer's amount the best way to get a precise indicator of your current song level, or is it bad because of how certain repertoires affect it?

Is it a given that, like a mage, a higher level bard will have a higher quality song given equal repertoires and instruments and charisma?

How does song skill percentage affect the song itself beyond you fail to sing it less?

Now once you understand the above you can begin to understand how to gear against a bard.

Is INT the counterweight stat to a bard song and CHARISMA? Edges imply that high INT characters, barring a certain edge, resist songs more easily independent of saves. INT affects what damage type Apocalyptic Overture picks, for instance, right? Does it affect the actual numerical affect of debuffs as well as the chance to land?

Is saves versus mental equal in effect to saves versus spell i.e. is -50 svs spell and -50 svs mental weighted the same on saves, or is the -50 svs mental going to give you more bang for your buck than the same amount versus spells? If it is in fact weight this way, is it correct that since alot of the most widely available saves against mental is heavy or inconvienient, you can get away with wearing less saves versus mental than you might gear for against a mage? (since in general there are fewer bards than mages anyway)

Does resist mental change the way you save against bard songs or increase saves, or both? I understand it decreases damage already. Fortress of the spirit warrior legacy does a similar change? Additional to the answer to saves versus mental above, is the benefit of saves versus mental on top of resi mental going to be dramatic or mediocre? Are you better off choosing one or the other and not both for a rough and tumble lifestyle in which you might encounter a bard but aren't 100% certain?