I read your post but I find that its difficult for us to help you decide. If you are asking whether Affliction/Demo is viable in ToT in terms of Heroic Raiding, then the answer is Yes. Many heroic raiders are running with Affliction/Demo and making good progress. In fact, both of them have similar secondary stat preferences (Haste,Mastery, Avoid Crit).
I don't think there is really an optimal offspec this expansion. All three specs are very very viable even at high-end raiding.
Ultimately, what offspec you choose depends on a lot on the needs of your Guild. And you are the only person that knows that the best. Are you having specific problems on certain bosses that require you to stick to Destro? Are you limited to Destro due to certain issues with raid composition? For Horridon, I can tell you that affliction is definitely viable for it. You don't need Destro.