I recently read that H670 supports three PCIe 4.0 M.2 NVMe SSDs....and that the B660 is only able to support one off the chipset itself.
Following info is direct from an Intel slide on chipset differences.
First number is for H670; second number is for B660. All other details on the slide are the same for both:
DMI 4.0 lanes; 8, 4
Chipset PCIe 4.0 lanes; up to 12; up to 6
Chipset PCIe 3.0 lanes; up to 12, up to 8
SATA 3.0 (6 Gb/s) ports; up to 8, 4 (my note: not "up to 4")
Maximum USB ports; 14/12
USB 3.2 Gen 1x1 (5 G) ports; 8/6
The H670 supports PCIe RAID 0, 1, 5; the B660 does not