Cirrus-Cirrocumulus transition clouds. Setup is controllable by a single "cirrus" PF cloud density (as far as seed and shape), though tons of customization can be done with the voronoi breakup internal node network. I'll post a file share when I think it's polished. They are 2D for speed. I wanted to test with v3 but it slows down so much due to the lack of density.
How do these look? Threw in a test image with the voronoi cloud shader plugged into a default v3 cloud layer (last image).