That's a problematic metric as well because we don't know how much area the assist circuit takes up. Modern high-density SRAM cells cannot operate as is, they need an assist circuit to compensate for variations. For example for Intel's 10nm SRAM, they claim 77% area effiency (https://fuse.wikichip.org/news/525/iedm-2017-isscc-2018-inte...). But without those values, just bits/mm2 or so is problematic.