I believe a C&J G width would be a BB Peal & Co. F width ( or EE width). Some C&J models have H width (EEE WIDTH).
I too struggled with the Peal Co. Shoes, specifically the perf. Captoe. The US 11E was a little too narrow, so I will have to go with a UK G width.
The same question arises for me, are C&Js a full size smaller from US to UK, or only half a size smaller? I believe the SA from the NY store mentioned it would be a full size difference, but I would appreciate more input as well.