Before I had the Wilbers rear shock I had the same setup on 4 day trip as you describe:almost the same weight for rider and pillion, OEM triumph top box and and ortlieb rack pack squeezed between swmbo and the top box. The shock was clearly under a lot of stress and the bike did not handle well, to be honest it was awful.
First action after that trip was to get rid of the top box, bought a bigger rack pack and in the end Givi panniers. The real break through was the Wilbers rear shock though. Did not help with swmbo: by the time that shock was fitted she had done the test and has her own bike now, so we rarely go on the tiger together now 😄