imo...and just imo
if you wanna try it go full shadow...its really the only way to make the shadow tree viable. Ive tried a lot of mixed shadow specs and there just isnt any real power there without going all the way into things. just going to mind flay or even going down to nab silence dont get the job done enough to warrent the other sub-par talent choices.
If we take a look at each spec ill say a few things I guess.
Spec 1: This picks up a great tool from disc, reduced stun is great. Renew is decent as well, although probably unwarented. The question with renew would be what else to spend the points on. The major issue is no imp devouring plague which is really the bread and butter of the new shadow priest movement and is the key to making shadow viable imo.
Spec 2: Its full shadow...not much to really comment on.
Spec 3: This is a spec ive tried a bunch. Picking up Mind Flay simply doesnt make up for the major losses in disc (as this is really a disc spec) such as bigger mana viability and youre losing fort and reflective shield and such, youre also going into shadow halfway but you simply cant get far enough to pick up Silence which might make the spec work. The increase in DPS is marginal at best, and while you do get a snare, I simply feel it is not enough.
point being
neither of those teammates (mage or rogue) really benefit more from a shadow priest than they would from a disc priest (well played disc/rogue is still best 2v2 comp imo, and I feel like both shammy and sl lock would make better mage partners than a shadow priest, or disc for that matter) so I see no real reason to be specced shadow for those teammates unless youre just bored of disc and wanna goof around. Both of your potential partners are there to provide control. Too many people wanna run in blasting and forget the vast amounts of CC already availible to the comp and the burst potential following a cc chain. You really dont need more DPS from going shadow, you just need calm focused play as disc ;p If by mage rogue priest youre talking about 3s, I think the same fundamental idea applies, you dont need the potential extra dps from shadow when your two dps are ccing. Disc still has pretty solid damage potential which a lot of priests tend to ignore.