So, I want to put a phylactery of positive channneling on my cleric, however, it is a headband slot and I need the slot for my casting stat. There is an Ioun Stone that grants an enhancement bonus to my casting stat, +2 same as my headband. Now, currently I get bonus spells per day based on my icreased casting stat, would this also hold true if I replace the headband with a corresponding Ioun Stone?
Yes, you'd get your normal +2 enhancement bonus to Wisdom if you use the Incandescent Blue ioun stone. It's balanced this way because the ioun stone costs twice what a normal +2 stat item does due to it not taking up a slot on your character.
Ok, so that means I also get bonus spells per day as normal?
A +2 enhancement bonus is a +2 enhancement bonus regardless of sources. It works the same on a headband as it does on Ioun Stone. Everything is the same. The difference comes in because the Ioun Stone costs twice as much, and by normal rules they don't come in a variant stronger than a +2, but you could probably convince your DM to allow otherwise, still at double cost though. Of course, if he's willing to agree to that you're probably better off asking him to allow you to combine both headband items into 1 item by multiplying the base cost of the less expensive item by 1.5.
"Permanent" Bonuses to Stats work the same way, regardless of what item/source they are.
If the duration is 24 hours+, you raise the effective stat for all purposes. (including bonus spell slots)
Shorter duration effects have much less effects, but that doesn't apply to your choices.
Ok , I just wasn't seeing where it states the bonus as "permanent" or "temporary". Is there text stating that the Ioun stone enhancement is permanent or is this information that has to be deduced another way?
Claxon, that is a good idea, I thought of it but wasn't sure if my gm is cool with it yet as i haven't asked but there are provisions for it in the core rulebook so i may.