So, if you're signed off in a 172 after completing your private ticket and continue your instrument training in a 172 you may log that time as PIC. But, if you do that time in a high-performance aircraft in which you are not endorsed or other such aircraft for which is not the same type as a 172 then that would be strictly dual time.

This is per our chief flight instructor as well as a FSDO examiner who even signed my log as having performed as PIC during a 709 ride.