The slots are going to vary, depending on your class, needs in terms of stat stacking, if you raid, and if your your raid (yourself or your guild) are capable and willing to do all of the achievements.
For myself, at 125, I use the Fully completed ToV ear on all characters, plus the NoS Back on all toons, however missing raid achievements to finish it out. The same goes for the LS neck, I have it x6, but my raid/guil;d is currently unable to complete the raid achievements *and* conqueror (largely because Artisan raid is still broken).
That's 3x evolving items in my group per toon. I maintained all four TBL items (No TBL raid cheeves for final evolve) until Tol-NoS era, depending on the class and slot. Healers replaced boots as soon as the focus wore out, solely because of the focus. Shoulders and gloves were replaced as I could during the NoS era or ToL if i had a chance to replace with better quality raid gear. The exception is the ring, which I've held on to, even on a raid MT, as it's still "viable" and moreso wasn't worth burning currency/DKP when the ToB ring is around the corner.
An interesting exception, although possibly due to magelo ranking systems, is that the "top serverwide monks" all generally continue to use TBL boots and gloves, some include the ring and shoulders in addition to the LS neck, NoS Cloak, and tov ear. I can presume this is only to try to stack as much hdex as possible with fortification/enhancement augs in the 18/19 slots.