Independently is what I'm after which, as I feared, maybe a learning curve too far at this moment in time!
Think about how YOU would move the servos different amounts at different speeds. You'd keep track of the last time you moved a servo, and where you moved it to. Periodically, you'd see if it was time to move each servo again. If so, you'd adjust the position of a servo, and record when you adjusted its position.
"Periodically" on the Arduino means every pass through loop. Time is determined by the millis() function. The other stuff is simple variables and if statements.
I'm powering the servos through the Arduino board (5v) and the board is powered from a bench top power supply
Servos should be powered by a separate power supply. They draw a lot of current - often more than the Arduino can supply.