For those who have not found the fifth page, I would suggest starting off with the last hidden page that was found -- gathering any possible clues from that and trying those clues -- and working your way back to the other hidden pages, if necessary.
The fifth link is not that hard -- so do not over-think it. Moreover, this thread -- as it is fifty pages -- does have some good guesses, which are at the cusp of finding the page.
Don't give up hope, yet -- some trial and error is, of course, necessary, but once you find the page, it will be that much sweeter (and apparent).
Good luck and Cerca Trova.
Cheers,
JTM