Try Bard/Evangelist/Shadow Mage (preferrably Wizard for the feat, but nothing is stopping you going Sorc)
Try it on PGCC and see how that works.
You get +4 DC on Illusion for GSF: Illusion
+2 DC from Shadow Mage
+2 DC from Evangelist (mind affecting)
For fear based spells: +6 when using conqueror's canticle before the spell
For non-fear based will save: +3 when using atrocious aria before the spell
Can go with 24/3/3 split, or 22/3/5. Can even get Divine Shield if you spec for it.
Trickery/Darkness domain maybe? For the immunity to darkness and skill bonuses.
Bard song should be at 30 with Eva with Divine Favor on.
Spells to take:
Phantasmal Killer - Your top DC illusion spell
Illusory fall - your second best, and AoE control
Shadow Evocation/Conjuration line of spells - for all the variety it provides
Darkness - your early game control
All theoretical though.
Shaman seems like a better option? But that's going to be Shaman-deep, not bard-deep.