Breaking 1 block per layer reveals 4 blocks around it. 1 block for 4: 400% performance. (This method is the best.)
Breaking 2 blocks per layer reveals 6 blocks around. 2 blocks for 6: 300% performance. (This is a 2x1 branchmine shaft for comparison with the above method.)
But this is only useful if you are looking for caves and have a good way of getting back up (teleportation).
This is the pattern (gray lines indicate block borders/edges):
Mining straight down with 100% coverage 1 zoomed.png (636 Bytes) Viewed 10929 times
This is how it tiles infinitely:
Mining straight down with 100% coverage 1 tiled zoomed.png (13.29 KiB) Viewed 12245 times
And some more images:
Spoiler:
Mining straight down with 100% coverage.png (97 Bytes) Viewed 10957 times
Mining straight down with 100% coverage zoomed.png (226 Bytes) Viewed 10804 times
Mining straight down with 100% coverage tiled.png (133 Bytes) Viewed 10755 times
Mining straight down with 100% coverage tiled zoomed.png (930 Bytes) Viewed 10895 times
Mining straight down with 100% coverage 2.png (374 Bytes) Viewed 10769 times
Mining straight down with 100% coverage 2 zoomed.png (1.32 KiB) Viewed 10894 times
Mining straight down with 100% coverage 2 tiled.png (905 Bytes) Viewed 10836 times
Mining straight down with 100% coverage 2 tiled zoomed.png (10.65 KiB) Viewed 11181 times
Mining straight down with 100% coverage 1.png (249 Bytes) Viewed 10775 times
Mining straight down with 100% coverage 1 zoomed.png (636 Bytes) Viewed 10929 times
Mining straight down with 100% coverage 1 tiled.png (936 Bytes) Viewed 10785 times
Mining straight down with 100% coverage 1 tiled zoomed.png (13.29 KiB) Viewed 12245 times
