DSGriffiths,
The Graham 2.2 as you have stated is a unipivot, whereas the JVC 7045 has gimbal bearings. It is surprising that you get the same results with both arms with the Decca. I have set up about 20-25 Deccas on half a dozen different arms and heard substantive differences depending on arm and which Decca model is installed, even sample variations between Decca's.
Martin Colloms of Hifi News had variable tracking results when using different arms - Linn Ittok, Naim Aro, SME V - despite all having good bearings.
These variable results concur with my own experiences.