The pairs I imagine CAN beat the Sannin are Itachi/Kisame, Nagato/Konan, Sasori/Deidara, and Tobi/Deidara.
One fact I'd like to point out is that if Konan or Deidara are prepared, the Sannin lose. Period. None of them can see chakra, so C4 would likely herald their doom. Also, if Deidara has multiple C3 bombs up, he could likely pressure the Sannin enough to let Sasori or Tobi take some of them out.
Konan, of course, has that tech. with 600 BILLION explosive notes, which could take out pretty much anyone caught in it (except Tobi). Pein uses Bansho Tenin to pull in two Sannin into the blast radius and sacrifices Deva Path, and boom. Pein and Konan vs. 1 probably terrified Sannin.