Because of several constraints on our stackup and line width, a 6mil
stripline trace yields a Zo = 29ohms. When I simulate a 29ohm,
unterminated line on our board (@ 10MHz), I see a pretty nice waveform,
albeit with slower rise/fall times (which is ok for the nets in
question). When I increase the Zo to 60 ohms, for example, I see a lot
of ringing on the same net.