If you're getting Vashj to 8%, she should be dead. Ask everyone to turn down all of the settings which may affect frame rate, and put spell detail down to half. We wiped there only because a significant number of players got screen freeze. With the settings on absolute minimum, Vashj died on next try. I really think if you're getting through phase 2, you have the kill....
After that, our guild chose to go to Hyjal, then BT. It was not hard to get 4 bosses in each (4/5 4/9 since attunement was removed, and we only raid 3 hours/night).
We're spending this week on Kael'thas. I hope he will die tomorrow. We added 2 hours on Sunday raid (leaving early) to give us extra time to kill him. If not, I will have a tough decision too - whether to go back to BT and Hyjal for a few weeks before trying again, because we cannot afford to stop farming Heart of Darkness for long. Plus, I don't like to bang our heads against the same boss over & over if it's not strictly necessary, and it's at the expense of farm content that we can use. If this situation comes up, I will consult not only the officers, but the core members, to see how they're doing and what they want.
Part of the podcast was also about how the speed of clearing is a form of progression. For BT, make sure everyone can reach 10k hit points buffed, and try getting the first 3 bosses on speed farm. About ADD, I don't know, my raid doesn't have it. Maybe mixing it up would help.