Ultra high temp ceramic grease is the correct stuff to use. With EVERY new car I acquire one of the first things I do is remove the plugs, apply ceramic anti-seize coating and replace. Then I know they will come out easily in a few years time. Lubricate the rubber connectors with a litttle silicone then they will slip over the plugs more easily. The other essential job to do with any modern GDI engine (which means basicly all latest generation gasoline engines) is to run the crankcase breather pipe (from the rocker cover on your GDI) to atmosphere or a can open to atmosphere and securely plug the inlet manifold port. This is to eliminate totally well-documented inlet tract and inlet valve fouling problems.
