I bit the bullet and got a set of Perpetuals.
I'm mainly a classical guy, so here is my review for anyone considering these strings as an orchestral/solo bassist.
To be as succinct as possible, I love them. I think that they have pretty quickly become my favorite set of strings that I've used, though I think they are still breaking in at this point. In the past I have tried flex deluxe, flexocor, bel cantos, and spiros. Out of these strings I found that I really loved spiros because they had an incredible ring and the largest sound of any string I used. This to me was really important, and why I liked spiros, but they have (as you may know) pretty heavy drawbacks in their response time, and brightness. I play on a new instrument (made by Mike Shank) so my bass naturally has a very bright sound, and at times the brightness of the sprios led to a brittle sound. Basically anything above the second G on the G string required vibrato in order to be warm enough to listen to. Flex deluxe and flexocor were both great strings in terms of response, but they lacked a singing quality that I really wanted for solo playing. Bel Cantos have that singing quality, but they don't really sound great to me, and I have trouble getting strong articulation with them. Now, onto my experience with the perps... They are pretty low tension strings. They have a ton of give, and at times I accidentally get them vibrating into the fingerboard which isn't ideal. However, they have that characteristic spirocore sustain, brightness, and volume, while being a tad darker and much much better response. Perpetuals ring forever, they have incredible richness and overtones, and I feel like almost make your bass sound like you're playing in a church or boomy concert hall in a small practice room. That being said, they have fantastic articulation response, and I've been getting a cleaner brush stroke than ever. If you are an orchestra player that loves the sound of spiros but hate the way that they respond, I could not recommend perpetuals any more. I think that these strings are fantastic for orchestra playing given the response, sound, and darkness, and I think that they are equally impressive for solos given the sheer amount of volume you can produce with them. When I was looking into these strings I heard them billed as "spiros with a darker sound and better response" and to me, that's exactly what they are.
Review over. Cheers.