Some numbers about hopper lag, for version 1.16.4.

Using command blocks, a 65x65 surface of these blocks was created, 4225 in total.

What Vanilla Sodium/Lithium/Phosphor
Empty world 1ms 1.2mspt
create 4225 hoppers, facing down 7-8ms 8.1 mspt
cover them with composters 4ms 3.6 mspt
cover them with droppers 4ms 4.3 mspt
cover them with furnaces 5-6ms 4.8 mspt
redstone blocks 1-2ms 1.3 mspt
redstone blocks + droppers 2ms 1.3 mspt
redstone blocks + composters 2ms 1.3 mspt
redstone blocks + furnace 2ms 1.9 mspt
  • Hoppers without an inventory above them are bad, although not that bad: 4225 hoppers in 25 chunks cause approx 7 mspt.
  • I did try having some loose items in each chunk but could not see a difference, although I am not certain I measured the furnace case.
  • Some kind of inventory above the hopper halves the penalty, but furnaces are a bad choice. Composters or droppers are good.
  • Best is turning them off by powering them.

Using the carpet mod commands tick health or tick entities gives more dramatic numbers. It seems the ‘Uncertainty Principle’ applies to Minecraft. I wonder what Heisenberg would think about that.