i dont visualize words during speaking. i only do it if its necessary for delivery. but not always. in my experience, thinking in images is fast but its unreliable because you may think that you know what you've imagined but you maybe mistaken. so i think in words instead and i crosscheck with images if they correspond words correctly. also what i do regularly is think of several words about what i want to say before saying, so that i had something to move forward to. what i have hard time with is always thinking beforehead. thinking in words is time consuming and you dont always have time to plan whole speech ahead. or even main points