If the distance to the object is farther, your rate of turn can be slower.
but the jerky movement still occurs with a slower turn rate, as shown in the last video.
Could the following line cause a problem:avoidance -= agent.Velocity;
I ask because it is not included in the OpenSteer source code but causes the agent to move way too fast without it.
Well, steering shouldn't make you accelerate over your maximum velocity. Everytime I've written a steering component (it's been a while though, so I might be missing some details) I made it return 2 things:
2) braking factor
The braking factor can be optional, depending on the feel you want to have. In the examples you showed, you just need to modify the heading of your cube.
If I understand correctly in the code you posted destForward is steeringForce? If so, from what you posted you only use it to calculate a turn angle, how would it make the agent move way too fast? Have you tried clamping your velocity to your max velocity?