I’m a computer engineer - a lot of programming, but also a writer so a lot of writing, and we also generally do a lot of writing in our daily lives - emails, chats, prompting… :D I am generally split between English and French writing mostly.

I use a combination of Dygma Defy with its awesome thumb cluster, along with macros for frequent series of letters (think “tion” and such) as well as chords using https://github.com/rvaiya/keyd/ . And I use the Optimot layout because I’m French, for English speakers, Dvorak is probably enough, but Colemak and many other alternatives offer various advantages depending on your usage.

As many have hinted here, it’s absolutely not only about speed. It’s about comfort, both physical and psychological.

Using the thumb is a great way to avoid moving the hands too much because now your pinkies don't have to reach keys on the side which generally causes a slight extension of the hand. After a year of using the Defy, I don't have any form of strain building up in the thumbs, even though I use them quite a lot - but still a lot less than other fingers.

Macros for short series of letters are very powerful in my opinion: it doesn't necessarily goes faster as it breaks the flow of typing, but you have a lot less keys to press which also minimizes errors. The same goes with chords using keyd (I know it’s originally not exactly designed for that usage, but it still works great at least for me) - less keys, less coordination.

Finally, the choice of keyboard layout is critical. Originally I’ve switched from the French Azerty to Bépo because I notices how much my wrists were moving when I was typing in French with Azerty compared to English in Dvorak. There was a huge difference and I could feel it in my bones after long sessions of typing. So yes, choose your layout wisely.

As a last note, typing speed does matter. But it’s not about typing at the 0.001% fastest percentile. Typing speed will not make you really faster, but you just don't want it to slow you down too much. Typically, you don't want to be in the position where your thoughts go so fast that you feel the frustration of not being able to type fast enough and losing some of your thoughts in the process. Besides, for coding it’s much more about having the right tools at your disposal: powerful auto-complete and suggestions, easy refactoring processes, keyboard shortcuts to do everything you need, easy access to symbols on your keyboard/layout, etc. Typing speed is rarely an issue while programming compared to when writing plain text.