Re: Impedence of trace
4 layer board?
What layer is the ground plane? Are we talking about a microstrip trace, or something more exotic like coplanar waveguide (two strips on the surface, like a differential line)?
By power planes, do you mean big sheets of metal that are between your top layer trace and the bottom layer ground plane? If so, then you have what we call a "kluge", ie no specific impedance. Your high speed signals will look "interesting".
Rich