Effective (for lack of a better word) lying is a skill, and requires some care.

In the case of speed/distance info, you want to lie upward to impress people, but you have to be careful to stay within the bounds of the plausible. Over-inflating the data defeats the purpose, since all you demonstrate is that you not only are lying, but are so ignorant that you don't even know the bounds of reality.

I have an automatic go/nogo filter for this kind of stuff. It weeds out the obvious liars, but I sometimes find myself wondering when folks just slightly shade the truth.