Option A seems okay, but what happend to minor discussion? And who decides when to create a new thread. It could mean loads of nonsense thread for little minor things, but on the same hand where else do you post these minor things?
Posts by Gtom/Andreos on 15/01 I'm not sure where you could post them?
Maybe a latest thread could remain (archive pre-2015) so that most people will be loading just the 2015 posts. Others years or a half year could be locked away, but visible to members?
These is opportunity to dilute the latest thread further? A REPAINTS thread could be an idea?