If i'm not mistaken, Chest, Head and Legs are the slots that get the most stats/ilvl, shouldn't they get the priority after the weapon upgrade?
The helmbreaker's medallion would give 1241 strength and 4135 crit for 15 seconds every minute. Up from 1152 strength and 3838 crit for 15 seconds every minute. So 74.25 more crit and 89 more strength. Upgrading a normal chest would give you 49 haste, 82 strength and 61 crit. Pants would give you 88 strength, 52 expertise and 64 matery. I'd say weapons > H tier > trinkets >= normal tier.