The rate at which commands can be send depends on the type of Phidgets.
For USB Phidgets, this depends somewhat on your machine, and can be up to 3-4 thousand commands/second.
For VINT Phidgets, this will depend on whether the device is isolated or not, and it's polling interval, and the size of the packets, and how much data the device is sending back. Isolated VINT Phidgets run at 10kbit with a maximum polling interval of 8ms. Non isolated devices run at 100kbit and poll at a max rate of 1ms.
For RCC1000, this is an isolated device. A command packet is 8 bytes, so this takes 8ms to transmit. The device will also be transmitting event data back to the library, and the VINT link is 1 wire so transmit and receive can't happen at the same time. There is also some handshaking overhead, etc.
So, you you can expect be able to send a command every 16 or 24 ms.
If you are sending a lot of servo commands, you should use the async version of setPosition to speed things up - this lets you queue up and send commands as quickly as possible without waiting for the response each time.