I would seriously avoid OcUK if at all possible. Their customer service is dreadful and they just seem to get away with the most outrageous breaches of consumer law. All they care about is debiting your card and then you can and hang for all they're bothered. They don't stock anything other than the big profit items (try buying a water-cooling barb or a small part for a Lian Li case from them) and when anything goes wrong the first thing they'll do is palm you off onto the manufacturer's RMA system which can take months to resolve your problem.
East Midlands Trading Standards should be utterly ashamed of themselves.
I would buy the 4Gb (2 x 2Gb PC6400) Patriot kit that Aria have for £185 at the moment as it does what it says on the tin. It doesn't overclock especially well, but with an E6600 you don't need much more than 800MHz/PC6400 anyway.