Guild Wars 2

I see that all ascended gear often has 2 of the same stat — one higher and one lower. ([Feather of the Owl]) Why is this? I head ascended gear can be upgraded. When this happens, does it go to the “second tier” of stats? Or does it just get upgraded with an infusion?

upgrading only provides infusion.

as for the 2 sets of stats, think about normal trinkets (actually most gear follow this rule). The come with a set of stats, but also has a slot for you to put in a gemstone to give more stats. Ascended trinkets is like having the gemstone pre-applied but also has an infusion slot.