I work pretty hard to keep CPU utilization in Maemo Mapper to an absolute minimum. You can probably increase those figures by a small amount with some tweaking to the Maemo Mapper settings, i.e. disabling auto-rotate, keeping rotation at 0 degrees (north is up), disabling announcements, and either turning Auto-Center off or turning Auto-Center sensitivity to the minimum (to reduce the number of disk accesses). And, of course, if you don't need the display on for the entire trip, you can tweak the "Unblack screen" settings to save more battery life (the "when approaching waypoints" option is perfect for this).

If you have no maps in your repository and disable auto-download, drawing of the track, and unblanking, then Maemo Mapper uses almost no energy in accessing/drawing maps, at which point it becomes a pretty minimal GPS tracer (both in functionality and in battery usage). It won't be as efficient as a command-line-only program, but it will get pretty close, especially since the screen is completely off.