Increased buff effect vs increased aura effect?

What is the difference between buff effect and aura effect? Is 5% increased buff effect the same as 5% increased aura effect?

And also, how much increased aura/buff effect do i need for an aura gem to effectively gain a level (if it's even possible)

Example: I want my purity of fire to give 5+ max resist, for that the gem needs to be level 23. Is it possible for that the gem will gain the effect of a level 23 gem while staying at level 20?

No difference if applying aura to yourself. The difference will be that your party members will only get the Aura Effect buff.

All increases from all sources add together. What percentage of increased effect would turn a 4 into a 5? I'll let you do the simple math :)

As far as effects of your auras on yourself go there's no difference between aura effect and buff effects, both kinds of bonuses stack additively and are virtually the same.

The game rounds down, so if you use a level 20 purity which has 4% max resist, to get an extra 1% max resist you would need to have at least 25% aura/buff effect.

Thanks guys! that cleared things up (: