I am in the same situation. I am playing with DX9 for now, but as you said it has strange jitters and crashes too after 30-60 minutes when zoning into cities with a lot of players (Limsa/Idyllshire).

DX11 just crashes randomly. Could be 5, could be 20 minutes. No other games (MMOs included) have this issue.

This needs to be fixed ASAP. It will make Stormblood unplayable and is the reason I'm holding off purchasing it (or renewing my sub at all).