Fitted some fresh new plugs and decided to try NGK copper plug instead of Volvo OEM Iridium plugs. They work great and cost next to nothing. Decided to try NGK K20TT 4606. Double checked the gap to be sure, they are correctly preset for the Volvo S80 2.4 / 2.5T.
Still have to get used to swapping out 5 spark plugs instead of the “usual” 4.