Yes. Depends. And this is understandable. People who speak quickly and clearly, naturally think just as fast. And a person who stretches out words, phrases, or even begins to select and remember words, I think, of course, thinks slowly. And probably his iq is lower. Although these are different things.
I'll tell you based on what I was taught.
The speed of mental speech is much higher than the speed of ordinary speech. Mentally, we are able to pronounce about 600 words per minute. This is the reason why people are distracted when listening to an oral presentation - they mentally speak much faster than the speaker. Therefore, we need visual stimuli, slides with additional information, voting, simulations, etc.
So the rate of speech does not depend on the speed of thinking, as far as I understand. No matter how you talk, thoughts are faster anyway.
An interesting and difficult question.
The speed of thinking depends on its intensity and "depth"; the more complex the subject of thinking, the lower the speed at which the brain performs them, due to the need to operate with a huge number of parameters.
Accordingly, the speed of pronunciation is also inversely proportional to the "computing power" of the brain occupied by the thinking process - frankly empty and meaningless conversation on some "vital topics" can be carried on extremely quickly and naturally, but just try to discuss something as quickly while trying to take integrals.
This is due to the fact that the human brain is in of his conscious activity is not multitasking, it also follows that if you often and quickly "work with the language", then being a "smart and thoughtful sage who utters the truth" will not work, as well as vice versa. You cannot sing a song at the same time and at the same moment fully reflect on the meaning of its words and meaning.
So, in general, the speed of thinking and the speed of speech are interdependent - for fast speech, thinking obviously must also be fast (since it is necessary to instantly select a stream of suitable words and sentences), but at the same time it will also inevitably be superficial (the classic division of resources into "quickly and somehow" and "very long and [not] qualitatively" ^^).
This is not to say what depends on what. There is indeed a correlation between them, but rather both of these components depend on the characteristics of the nervous system - these are primary signs that have a physiological basis, to some extent they are described by the concept of "temperament". So people who can easily speak quickly really most likely have a great speed of thinking.
If we talk about acquired signs, then the speed of speech and the speed of thinking can be developed. And it is very likely that by developing one, you will inadvertently develop the second.