Just thought I'd post some of my thoughts based on recent experiences.
I first tried the Perps about 4 years ago and liked them initially, mostly due to the playability. After about 9 months, I felt as though they'd lost something so I changed them out.
Flash forward to last October (see earlier in this thread) I tried them again in a mixed set. Regular Perpetual G, D & A over Spiro Weich (S42) E string. This was coming from a set of Spirocore Mediums (S42). The main reason I changed was because I got a regular gig with a Big Band that plays once a week on top of other gigs (weddings, festivals, special functions, etc.) and wanted something lighter but without the brutal break in Period of Spiro Weichs.
The Perps sounded good on my bass I I definitely liked them, but it took me a while to realize they lacked a certain "punch" both acoustically and through my amps. So about a week and a half ago I put on a set of 3/4 Spirocore Weichs, hoping they'd be somewhere in between the S42 Mediums and Weichs (which, to be fair, they are).
On my bass and the way I play I noticed these things. The Spirocores have more "punch"/"oomph" and more depth, especially in the low end. I know every player and every bass is different, but these are just some of my observations. I do really enjoy going back and reading my old posts to see how my opinions and ideas have changed over the years.