I'm sorry to tell you but while demonology has better dps according to simcraft, this is only for
1) fights with minimum movement ( like baleroc)
2) heavy aoe fights ( like rhyolith)
On every other fights affliction performs better then demonology because of the small loss of dps when moving and because of multidotting.
Not only that, but your dps is a lot less dependant on your doomguard, the dps loss of having your doomguard die, being unable to open with doomguard or not using him for the full duration will be a smaller
should you decide to stay demonology as mainspec, i'd go with the darkmooncard volcano and moonwell challice.
Also know that doomguard is a bit buggy and it really wouldnt suprise me he gets fixed ( which will result in a dps nerf)