Mind you I don't have a good offhand (or main hand really but at least its an epic lol) and trinkets have been pretty crappy for me too. I'm in the process of crafting the belt too. Am I gemmed & reforged properly?
Do note that each reforge and regemming is done based on current stats, so once you have more gems to work with, multiple uses of the tool will present more information. Shadowcraft can also help you determine how much of a gain proper weapon enchants are compared to the cheaper options out there, so you can make an informed decision.
Atm you're under the boss (93) specials hit cap, and you're reforging out of hit, so that's an easy fix. That's the only glaring issue; a belt buckle for another gem is a big +, of course, but if you're expecting an upgrade in the next week, it can also be an expensive piece to pick up for a single gem. Talents - outside soloing (nice movement boost), Shadow Focus is generally your tier 15 choice. Leeching poison has little effect for assassination as well, so Elusiveness (damage reduction) or Cheat Death (oops I F'd up) tend to be better options, but in RF and low-level play this is a smaller concern.