Thanks for the info on the Scythe Gentle Typhoon's guys.

Initial results do seem positive as they seem to beat the slipsteams in terms of cooling power to noise. That is, if I'm reading that review correctly as I found their diagrams a bit confusing. They use the same colours for completely different fans and the legend that was provided was a bit strange...

I'm not sure exactly how they tested it and it's too bad they compare them against the slipstreams as there will be some restriction in my case (i.e. fan filters, air duct etc.) and the slipstreams aren't great under those conditions.