Thanks.
Three PCI-E power connectors is way too little amount.
And you would need to underclock it if you are running it with ~600W PSU.
Based on my experiences with Avalon6 you could try with 2 connectors per board and one for controller -> total of 5 PCI-E connectors and make sure that the connectors won't heat up. Just make sure that the wires are at least 16AWG.
Are you asking this because you have other plans for the Enermax Revolution 87+ 1000W PSU that comes with this?
edit: Oh, I saw your posts in sidehack's thread and realised the reason.
For his version of S7-LN Corsair CX600M would be enough but you still have quite little amount of PCI-E connectors.
5 would be great.