I noticed that using the test configuration I get a lot of variation in raw heading info.  Fortunately I didn't include a test point.  After soldering to the DAC pin and attaching the 'scope I saw the problem immediately - noise.  Doing a little research on the PJRC site I found that biquad noise has been an issue before.  I may drop down to an FIR filter to quiet things down.  That may mean adding some prefiltering to the FIR filter to get the requisite brick wall filter performance.