No shoes:
Level 3 - non-crit
Level 4 - non-crit
Level 5 - Only crits <--- 50% of a Sharbha, an elemental, and a few Manticores
AF3+2 shoes:
Level 2 - non-crit
Level 3 - Only Crits <-- elemental, several manticores
Crit rate +1 Wivre gorget:
Level 1 - Non-crit
Level 2 - Only crits <--- all of a Sharbha, an elemental, and several manticores
Remember that it's possible to get unlucky, but I could not for the life of me force a non-crit with 5/5 Feather Step without shoes on. This conflicts with my earlier sample that showed a ~14% crit rate at a dDEX of 8 though, so maybe I'm wrong! :D
If I was a betting man:
No shoes: 1%/1%/1%/1%/1%
Shoes: 3%/1%/1%/1%/1%