Theoretical maximum speed of typing

It is not safe to say, yes, it is polemic to say that "QWERTY is enough good."  You see, we are keyboad enthusiasts, hahaha...

The rest of us never think such a thing, but if they were to come across the QWERTY skepticism, they will view that with suspicion, I guess. No one believes that QWERTY is the best of all possible keyboard layouts, but "QWERTY is not enough good" is an extraordinary claim for them.

Why is it? What rules are applied to determine that?

I naively used to think that it comes from the cost-effectiveness of optimizing keyboard layout. We can get some effectiveness by swapping a pair of keys. For example, QWERTZ and AZERTY are made from QWERTY by such a way. Swapping one pair, two pairs, three pairs.. The law of diminishing returns applies. When the effectivenss becomes lower than the cost of the key pair swapping, it is enough good: This is the cost-effectiveness hypothesis.

The hypothesis isn't entirely invalid, but now, I tend to think that the bottleneck lies in our brains rather than our hands. The bottleneck determines a "passing mark" of keyboard layouts, I think.

The new hypothesis came from my experience first. I designed a novel Japanese kana layout two years ago. Theoretically it makes possible to type as fast as speak without hassles. But in reality, by typing such speed with the kana layout, I found that my brain is in a hassle instead of my hands! Now I'm leaning toward that typing faster than speech (without hassles, i.e. sustainable for a few minutes) is a special skill like tongue twisters. It is a good exercise but not a practical skill except for some specialists like voice actors.

Today I found a paper about the information throughput of a human, "The unbearable slowness of being: Why do we live at 10 bits/s?" (2025). I think that the paper suggests the new hypothesis. Typing speeds exceeding 10 bits/s (120 WPM) is a special skill like tongue twisters, and 14 bits/s (170 WPM) is a big hassle even for specialists. The difficulty is the same regardless of the keyboard layout used.

10 bits/s, 120 WPM without hassles, is a "passing mark" of keyboard layouts, I think. It is safe to say, under this rule, QWERTY is enough good.