No, OCUK and OCZ are not the same, OCUK is owned by Caseking.de and only sell stuff in the UK. Their PSUs are probably not worth bothering with.
AMD recommends a 600W with two 6pin PCIe connectors for a system with two 7850s. That number has to account for very power hungry systems and/or low quality units which cannot deliver what they claim.
So you can go lower than the '600W' number as long as it's high quality and it has a large proportion of the wattage number available on the +12V rail.
Having had a quick look at 7850 system power consumption I believe that a 450W PSU with two 6pin PCIe connectors would be more than enough for a system with two 7850s.
The Corsair CX600 (V3) hopefully is an improvement on the V2, if it is then it is a good enough unit. I don't know much about it yet though.
However for a similar price I think this is hard to overlook, considering that it is, AFAIK, comparable to the Corsair TXM series:
OCZ ZT Series 550W (£50 @ CCL Online)
http://skinflint.co.uk/692688
Independent voltage regulation and modular being it's major benefits.