What machines are runnung local servers? Physical or some Virtual?
I use an OPENVPN network for communication (there are 100 PC's in about 20 Companies in multiple locations and one big company with there own OPENVPN network with 160 PC's in 40 locations connecting to there own OCS server via OPENVPN network), this is the most secure and quite easy way to connect all servers without making any thing like a proxy servers :)
If you are interested I can help you to configure one :)
Up to your connection it depends what you are gona do using OCS.
If you wish to use a deploy service for installing new software every day I suggest above 300Mb but if you wish to do only a data collecting it does not need much, esspecially that you can set connecting interval in OCS. I have go a GSM with about 50Mbit connection without external IP address at home and I collects data from all mentioned PC's via OPENVPN client and the OCSserver is a USB stick installed Ubuntu on a silent HP Thin client for 10$ :)
So you see OCS doesn't need much to work.......