You rate the aluminium Cayman HF above the Cayman Carbon. What makes it better?
Are you saying that you add a rubber pad to the the loading butt? Is this an Omer accessory or did you make one? I cut a piece of rubber from an old flip-flop/thong sole to fit snuggly in the back on one of my Omer XXVs (there is a distinct lip which looks like it might be intended to hold a pad - but equally might be intended to bite into your wetsuit/wetsuit's loading pad). But after a quick test I decided to upgrade the straps on my "supplementary loading pad" (an old flip-flop sole that straps to my chest under the wetsuit) instead....
... the loading support is better on the HF since one can add the rubber butt...