I don't know how PS4 compare to MPSS, but I suspect the MPSS is a better tyre in the dry and on track, but the PS4 is probably better in the wet.
PS4 will undoubtedly be a lot cheaper than MPSS though, so maybe that would swing the decision.
My M135i uses BMW OEM MPSS, so I always use those but would like to try PS4S if they were only available in 18". Apparently they WILL be available, but I don't know when.
When I spoke to a guy who works in the tyre industry and with Michelin the response on PS4 vs MPSS was this:
Road car: PS4, it turns on quicker and better in the wet, some of the PS4 sizes are actually PS4S, which ones however well your guess is as good as mine. They said dry wise you'd be hard to tell.
Weekend / Track car: MPSS, better subjective feel, better dry lap times etc.
In short from my conversation with them if subjective feel is a priority get the MPSS.
P.S. I am still running PS4S and though they are good, I don't trust them, the MPSS always gripped hard even from the first yard, whereas PS4S seem to take a lot more to switch on, but my experience will be different as my rear tyre is the K1 tyre and the car seems vague in the rear at times and then sticks like glue at other times or just lets go. The front none K1 tyres however are fine but again I feel MPSS actually gave better feedback. I think PS4S will probably give best lap times, but MPSS is more fun, more communicative and inspires more confidence.
