After asking this question yesterday, I started thinking about how since picking up my second '06 Infiniti G35 Sedan in as many years, I've noticed that with this engine (145k miles), when I leave the clutch engaged and the transmission in neutral, the engine seems to 'lug' to a stop.
I started experimenting with the other method, and noticed the engine spins down more smoothly and quietly when I put the clutch pedal in before shutting the car off. My previous G35 (which was tragically taken from me by way of a careless driver with 94,995 miles on the dash; no I'm not bitter why do you ask?) I never noticed a difference. This G has an aftermarket clutch/flywheel combo that is a few lbs lighter than the OEM clutch & DM flywheel I installed on the old G.
Could the lugging to a stop be a symptom of a larger problem, or a derivative of high compression and lighter than stock components? If it is due to lighter components, wouldn't disengaging the clutch exacerbate the problem?