I've seen several players using Permanent long E with Bel Canto ADG. If you use this setup, I'd be interested in hearing why.
One guy in the LPO used Permanent long E with belcanto ADG, Evah Medium and then weich ADG. He found the feel to be tight like a spiro but less harsh under the bow. for what its worth he moved on to a spiro Light long E and likes it more
I have had success with this combination. If you are happy with the top 3 bel cantos, but are wanting more clarity, or color, or volume, or "something" from the 4th string, this is a good option. I also recommend what Sam said, the light Gauge 4/4 spirocore C. Both options are trying to solve the issue of a lack luster 4th string. Both take about a week of play-in time before they feel safe and even. I currently use the 4/4 weich Spiro C, as I feel it has a better contact point similarity to the adjacent bel A, whereas the permanent C felt like it needed a higher contact point than the adjacent Bel A.
I like Permanent E or E/C in a variety of arco applications. Tonally, they can be a great match for Bel Canto A,D,G. Good luck! Let us know how it turns out.
As others have stated, I enjoy the clarity and ever so slightly brighter “edge” (not sure if that’s the right word, but hopefully another Permanent low C user will know what I mean) it has. To be clear, it’s by no means a bright strong, per se, I guess it’s more about how clear it is for having such low frequencies.
Got the Permanent on-it's kinda blatty right now, but there's time to let it settle.....my nearest possible gig is in January.