22,500 DPS is a theoretical absolute minimum amount of DPS required to kill Deathbringer Saurfang (if you never let him heal, which is basically impossible).
Your tanks should be able to generate a marginal amount of DPS themselves, usually between 2-3k each. One tank should be dual speced DPS for single tank encounters. One healer should be dual speced DPS for two healer fights.
Your 5 DPS people should be able to do around 4k DPS or higher, you would like their average DPS to be around 5k or higher (so take a 4k, you best have a 6k to balance it out). Most raids killing the first four bosses have around 30,000 raid DPS or higher. That's roughly 5k DPS per DPS raid member, and 5k between both tanks.