The "machine-gun" sound of Spanish is more due to it being syllable timed, while English is stress timed.

https://en.m.wikipedia.org/wiki/Isochrony#Syllable_timing

Spanish also has heavy syllable merging, even across word boundaries. (Vowels merge together and hiatus turns into di- and triphthongs.) This reduces the number of actual syllables in speech.

https://en.m.wikipedia.org/wiki/Synalepha

When simultaneously translated English to Spanish, my translators complained because I speak fast, and they'd tell me they can't keep up. When I slow down enough, I end up losing my train of thought, so I had to practice speaking slower.

Also it might differ Mexican Spanish vs Castilian, where I didn't get much of a complaint by Castilian translators.

Your scenario introduce 'translation' as an additional task. I wouldn't be surprised if that ends up being the bottleneck, rather than anything specific to either the input or output language processing.

For me, it's not so much losing my train of thought but it drops me out of any sort of real conversational mode. At which point, I can feel like I'm giving up any sort of real engagement and just saying words.

(Though, in my experience, simultaneous translators I've worked with and listened to are pretty good. They seem to usually do a better than decent job even for speakers going along at a "normal" pace.)

> So the bottleneck would appear to be, not the physical limitations of communication, but the rate at which we can structure information to be consumed by another mind.

Yet the way in which we must structure information surely plays a role in how quickly we can do it, right? I can certainly read faster than I can speak, and I'm also confident that I can read with full comprehension faster than I can listen with full comprehension to someone speaking very fast, like at the end of a medicine commercial or the Micro Machines guy.

Take for example a physics teacher. They are fond of drawing diagrams because it's a quicker and easier way to refer to the concepts in play than relying on words alone. If we had the capability to project the imagery that accompanies our thoughts so that others could see it, I suspect we'd have to do a lot less talking. And in fact we practice this already with feelings and body language--most of us know when we've committed a faux pas before anybody says a word about it.

The same goes for programming: my thought is "i want to get all of the user's preferences", which is surely faster than finding where to put the query, when to call it, and then testing its correctness. This is one of the things that Alan Kay and Bret Victor go on about--getting the machine to be usable at a level that is closer to the problem space than to machine code. I understand what you meant, that typing at 300 WPM won't help you to design a system. But a visual development environment that actually works probably would, because it would let you work at a more conceptual level most of the time instead of typing magic words into a terminal.