I've gone from PSS to PS4, and for me PS4 have the edge in colder, wetter conditions.
PSS were phenomenal when you'd got some heat into them and the road was dry. They seemed much more of a genuine summer tyre.
PS4 still function well at that tricky point, say 7 degrees or colder, in damp conditions. I dare say in conditions ideal for PSS, PS4 might not be quite as good. But we're not talking night and day here.
One thing also worth mentioning - when the PSS were down to about 3mm they really seemed to have lost a lot of straight line grip. I could have got more miles out of them, but switched to PS4 at that point, and immediately got that grip back. Make of that what you will.
I highly recommend PS4.