It's been done large scale.
And small scale.
bobsaq3 and sidehack are spot on at stock/factory clock rates.
We prefer to allow a little more head room for OC'ing the Prisma's and hence have migrated to one DPS-1600BB per Prisma.
OC'ing a Prisma only makes financial sense if the cost per Kwh is low ($0.08/KWh or less).
Then there are the heat dissipation issues that come with filling a room/Data Center with OC'ed Prisma's.
Pursuant to that we are prototyping Open Bath Immersion (OBI) cooling using the 3M Novec Engineered Fluids in custom built polycarbonate immersion tanks.
With the ultimate goal of immersing 32 OC'ed Prisma hash boards, controlled by an RPi w/wireless, in an OBI tank powered by 5 DPS-2000's.
Power consumption should be ~10Kw per tank and dissipate ~32K BTU continuously, enough to heat the average American sized home in a Minnesota winter
AND GET PAID TO DO IT.
The residual/excess heat could be used to heat a garage, heat a driveway, heat sidewalks, melt snow off of the roof, heat a pool/hot tub/fish pond, etc. . . . . . .
Our Youtube channel (PlanetCrypto) has some videos of our initial testing.
Initial testing of 24x Tube Erupter boards in a Walmart fishtank:
http://www.youtube.com/watch?v=meOf0FJBkGAhttp://www.youtube.com/watch?v=y_yfHJ8yoh8A polycarbonate immersion tank with 2x Bitmain S3+ hash boards:
http://www.youtube.com/watch?v=gcb9TyQP5ZAhttp://www.youtube.com/watch?v=fStHV_Q-x7sWe no longer power the fan in the S3+ tank as it is not required for condensation.
The heat generated from the S3+ tank supplements the in-floor heat in our little DC.
We have laid PEX in the ground outside the DC as a place to dump excess heat in upcoming expanded systems.
When we get a 32 Prisma board system up and running we'll post some vid's on the channel.
I have wanted to do it myself and have come up with a few designs for tanks, but don't have the capital to get started. Good luck.