Orbx Sydney has almost no FPS hit (unlike freeware Sydney which is really bad).
In the Orbx version, on the water, you can get under the bridge with a lot of throttle but if you go slow you get stuck.
In the air with collisions enabled you hit an invisible obstruction.
You CAN fly under the bridge if you turn collisions off in accessibility, or go into dev mode which disables collision detection (and also disables the logbook) automatically until you return to normal mode.
