@philipma, don't forget to factor the Pi that's separate.

You still need a Pi for each of the RK-Boxes and a beefier PSU as well.

With the S3's power draw at 390W, you can get cheaper PSU's for each, or fit more S3's onto a large PSU.

Can't say the same for the Rk-box which could possibly be more than the hypothetical 480W stated.

Also, if you want the most hash possible, you know you'll be able to overclock the S3 if it's anything like the S1 (which it looks like by all accounts and specs).  So probably closer to 550 GH/s perhaps.

So let's say 5 TH/s for arguments sake for the 9 S-3's you gave in your example.

That blows the Rk-Box out of the water and out of the atmosphere at the same time.