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There is no unambiguous way to answer this question. In relativity, you can only define velocity on small distance scales. For example, there is no well-defined way to say whether a distant galaxy has a certain speed relative to our galaxy. You can say it's moving away from us, but if you like you can also say that the space between us is just expanding.
If you go through the wormhole and observe your velocity relative to nearby objects that you're passing by (i.e., you confine yourself to small distance scales), then you will find that your velocity is always less than c. On the other hand, you can arrive at your destination earlier than a beam of light that got there without going through the wormhole.
A simple example is an expanding universe that is closed, i.e., that wraps around on itself in a circle. This is like a balloon being blown up. You can walk to school in the morning and get there much faster than a ray of light that was emitted from your house and wrapped around the universe before finally arriving at your school. Does that mean you went faster than light? Well, it depends on what you mean by faster than light.
Yes, any wormhole is definitely a potential time machine. There is a good discussion of this in the final chapter of this book http://www.amazon.com/Black-Holes-Ti...8924987&sr=8-1
, which you can look at using Amazon's "look inside" feature.