This will depend on the material, end mill that you are using, and whether you are using a spindle or a router. The stepping motors and the mechanics on the blueChick (and the other machines as well) can move the machine very fast (x and y about 700 ipm rapids).
You will need to refer to the manufacturer specifications for the speed on the end mill with the particular material. The Onsrud end mills sold here are of top quality and can generally go faster than standard end mills. If the reliefs are in wood, you will be able to machine around 200 to 80 ipm depending on the wood and the depth per pass. Generally, you want to rough out most of the wood with a roughing end mill then finish off with a finishing end mill with a small tip and a small step over.
If you are using a router, the speeds will be slower than a spindle since the spindle can handle more torque and the torque is compensated with the VFD (Variable Frequency Drive).
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What's the maximum speed at I can machining reliefs without lost steps with BlueChick?