Compare:

• level@7 against classic-level. To test the native part (now using encoding options instead of *asBuffer). Not expecting a change here.
• level-mem + subleveldown against memory-level + sublevels, with json encoding. To test the JS part. Expecting a slight improvement here, though it might only surface in real-world apps (with GC pressure) rather than a synthetic benchmark.
• Batching on level-mem against memory-level, as it removes two (or three, with sublevels) iterations of the batch array.

A quick benchmark is enough (of reads and writes). It's just to check that performance is equal or better.