Relic to Ancient DPS priority?

I've been sitting on the ancient selector from Church for a while now and plan to use it when Belgardin releases. I know we're also supposedly getting another one as a gift soon, too?

Either way, since I already have 2/3 of my Order cores Ancient already, I was wondering if there was any tool or way to work out whether getting the 3rd is best, or getting Flashy Attack, Smoldering Strike or Attack? Thank you!