Personally I prefer to have all the same so you get the full benefit of the Michelins. Also found a lot of the interior rattles calmed down. I know it is wasteful to bin tyres with so much life left and believe me, I don't like opening my wallet unless I really have to, but I think it was well worth changing all four.
I've decided to bite the bullet Watts and have all 4 changed to PS4s. I checked Halfords/National, Asda & Blackcircles, but Kwik Fit are doing 10% off and are my nearest garage. ATS were slightly cheaper, but further distance to go.
So, 4 new PS4s fitted today at ATS/Euromaster. Just over £600 for all 4, as they have a Michelin offer on. Early doors, but I've noticed how quiet they are. I'm selling the two rear P zeros in the for sale section, for a nominal amount.