Mining pools communicating outside of network Does anyone know of any papers / evidence of bitcoin mining pools communicating outside of the bitcoin network for financial gain? It seems plausible in practice, but I am not sure if that has occurred. 

To be clear, I mean two mining pools sending blocks to each other outside of the network. This would give them a head start / be faster than using bitcoin's diffusion process.
This is definitely being done. One such network is FIBRE.

Obviously, miners want other miners to build on top of blocks they've mined as quickly as possible to increase the odds that their blocks will not be orphaned. And miners also want to get new blocks and start building on them as quickly as possible for the same reason.

So miners have every incentive to send and receive their blocks as quickly and as widely as possible. The bitcoin network is built to exchange blocks, but it's not its top design priority. So large scale miners use purpose built networks optimized for just that task.