I have not that much experience with this combo. But I played this setup last night with my roommate and while he is in some S2/S3 gear I am mostly in S1 gear and S3 gear from honor. We played this setup few weeks ago and didn't think it was any good, we were hitting a wall at 1700 and just stopped playing.
Yesterday we started playing again at 1630 and we played from about 4pm to 3am and finally got over 1850. We actually have a positive win ratio against warrior/druid, a team a lot of people have problem with. What I would do is sap the warrior, have my teammate trinket+dot the warrior full up and I would then either cheap shot the warrior or wait for the druid to come out of stealth and we would then go all out on druid. I would have to use every single cooldown to get the druid down as fast as possible. Stunning him in travel/caster form is extremely important, as you will do alot more damage in that phase. Vanish/shadowstep does do wonders against a druid running away.
We also are fairly confident versus rogue/mage, but it's still pretty hard. A warlock/priest is basically impossible. We tried going on the lock pain surpression just stops us. We tried going on priest and sometimes it works but mostly they just outlive our "nuke" (it's kinda hard to nuke with sl/sl and shadowstep ). Priest/rogue is hard too but we just have to go for the priest in that case and I have to try to keep the rogue away from warlock as long as possible. We did not meet many warlock/druid teams.
Hunter/druid is also tough but he would again dot everything up and we would focus on the druid if the hunter is BM. If the hunter is MM or Survival we would focus on him and maybe get a good fear/blind/vanish->sap going on the druid or we would switch target if the opportunity arose. Shadowstep is amazing for a fast swap.
I know see the power of this combo and will enjoy playing it alot more. Kinda undergeared for 1850s atm with 4/5 S1 and 1/5 S3 with S2 mainhand and S1 offhand, but in a few weeks it will be different I hope . Also, being in the same room as your partner helps a lot