You can click continuous timegraph icon on the metrics page. The last(7th) icon starting below the menu bar. That will give a single line instead of 7 lines.
Is it possible to look at Performance Manager data over time?  I'm not fond of the 24-hour window that everything seems to work with.  Right now, if I choose a week, it produces an averaged out 24-hour period.  I'd like to have a graph that shows me performance on an hourly basis for the past week.  The only way I've been able to do something like that is to open each day individually which produces 7 distinct graphs.
General question about Performance Manager