Ran on a 10 core Mac with an M1 for 5 days. Found 15 6 character npubs and none with >= 7 characters. Found the first 6 character one in 1.3 hours.

Have been running for another 6 days on a 12 core Intel Linux workstation and have not found any >= 7 character npubs yet.

The jump in difficulty from 6 to 7 characters is impressive.