I did get the Terreno Mix's and with the awful weather we've had here recently have tried them out and in mud I don't think actually any better than the GK - SK's.
That said I do think they roll beter on tarmac so will find something better for the mud / winter and keep them as a summer tyre where we do more tarmac mileage in percentage terms .. thought I'd update in case anyone else googles tyres for mud and finds this thread.