I always thought George P. had more or less the largest collection. No particular reason except for the fact that he lived in Tokyo (still there?) for a while when it was relatively easy to find any kind PCE stuff.
Unfortunately for all of us, George seems to have disappeared off the face of the planet (tragic since he was holding a few PCE CDs for me, one of which I have still nto been able to find a replacement for).
No one has heard from him in 4-5 years.
But yes, he did have not only a complete collection (minus some of the really rare stuff), but was also going for a collection of Unopened PCE Stuff. He had the Off The Wall Prototype for a while -- I do not know if the one that sold on eBay last year was the one he had or not.
(and I have the Game Lab magazine that features him too -- great images).
-bt