The 760p models seem to be Intel's high-end consumer models for 2018, while the 660p feel more like a mid-range variant, which integrates QLC memory and should cut the prices in half.
https://www.notebookcheck.net/Intel-s-upcoming-760p-and-660p-QLC-PCIe-NVMe-SSD-specs-get-leaked.278266.0.html