Hi, 

Safest-effective speed is the one you can handle without putting yourself at risk. You must perform risk assessment to see if your process represent any danger. 

People programming industrial robots usually cap under 250 mm/s as absolute maximum for programming open fence. This is also a good maximum for cobots. 

Even better than trying to go fast is to be efficient. Using Active Drive, part of "Force Copilot" for eSeries and CB Series with FT300, you can go where you want faster than with the arrow or with the UR Freedrive function.
"Active Drive" allow you to guide the robot rapidly and accurately up to the point. Note that we still use arrows for the retracted point and Freedrive to clear the robot away fast.

"Active Drive" run with the speed slider ranging from 50% of speed up to 100%. 

On the side of safety, slower is always better. And if time gets in the context, it is always better starting slow then accelerate progressively than to start fast and hit someone or something and break anything. 

May I add to avoid pinch points and pointy objects inside the reach of the robot. Always avoid being between the robot and a static object the robot can reach as a wall or a pole holding a static camera.  

Program safe, perform risk assessment and enjoy Cobots with Robotiq products.
Hope this helps. 

Regards, 

David Gouffé
Integration Coach
Coach en intégration