As always, use the various tools available to determine your own unique break even point. But yes, you need almost every single piece to be BiS before dropping 2t8 becomes worth it. For my own calculations it only becomes worth it when I can replace the last 2t8 pieces with very well statted ilvl 258 pieces. I would not be surprised if your own results were very similar.
While gearing up (TOGC 3/5) it seems like I can't get rid of my 2T8 bonus.
Currently, I wear T8 helm and gloves, 2 pieces of T9 (shoulders + legs) and Mjolnir + DMC.
Since I'm lacking a lot of small hit upgrades and can't get my hands on any legs with 3 sockets in the near future, I decided to get the T9 legs (link to full equip).
Am I missing something here (as long as the simulator is right) or can 2T8 only be dropped after obtaining almost every BiS?
Since I could always build my equip around 2 pieces of T8, one could even assume that it can't be dropped until the stats on those two slots surpass the set bonus on their own (or until a better set bonus is available, of course).
This just doesn't feel right, but where is my mistake?
I was in the same situation a few weeks ago. Eventually I managed to drop 2T8 when i got my first piece of T9.258 and the 258 beasts legs; running with 4T9 (258 helm/chest) and the 258 beast legs now, tho switching back to my T8 shoulders/gloves would only be a 10 DPS loss according to Rawr (planning to replace the T9 gloves with the 10man hc ones). In my opinion before you kill anub25hc you shouldn't worry about replacing it at least.
On a side note, I discovered a bug in anything25's built which seems to cap the output to something around 6828 DPS. I already sent him a private message regarding this issue but I haven't recieved an answer yet.
I'm not very familiar with the FBN source and couldn't find the issue myself after a quick look.
I thought I mention it in case anyone else is using this built.
This wouldn't be the first time someone took a vacation and never played WoW again. If anything or someone else picks it up, that'd be great; however, SimulationCraft looks like a lot more stable, customizable, and personalizable simulator right now.