AS: "I'll settle for a Priest of Osiris from any time before Dynasty VI..."
Again you are avoiding the issue - why?
The name of Osiris is securely attested in the archeological record around mid Dyn 5, where he has the epithets, 'Great God' and 'Lord of Maat' - so he was clearly a very important deity already mid Dyn 5. A possible less secure attestation may be from around the beginning of Dyn 5.
He was probably around way before this time but no one knows for sure - explicit evidence has not been found - only indirect clues.
I haven't come across a priest of Osiris anywhere in the OK, but there may be some mentioned somewhere of course, so why would you "settle for a Priest of Osiris" What has this to do with evidence for your 'exclusive massively dominant cult of Re at Giza'?
To back up your claims you should have evidence of priests of Re, 'Followers of Re' etc, just as Horus had in Dyn 4 - in Dyn 5 there were priests of Re, so surely there must be huge numbers of them in Dyn 4 where your 'exclusive massively dominant cult of Re at Giza' was active.
So just answer the simple question - were there priests of Re in Dyn 4 or not - it would not surprise me if there were, but in my research using very limited resources, I have not come across any so far - but you have come up with the theory, you probably have access to better resources than I do, so surely you should know.
CT