As far as I know, he should have worn a 17000 and there is also a picture of Messner wearing a 17000:


(Source: oysterquartz.net)

I´m not sure, whether this picture was made during his everest-expedition 1978, but it definitely does not show Messner on the everest-peak.

What can be taken for sure is, that Messner wore a 1655 on the peak of the Nanga Parbat.

Regards
Matthias