Typical speech is about 150 wpm, and someone making an effort can talk faster. Even the fastest typists on standard QWERTY-type keyboards have trouble keeping up with average conversation. Transcriptionists use specialized chording keyboards and can type 200+ wpm in a dedicated phonetic one-chord-per-syllable shorthand with abbreviations for common words.

I have no idea how well current speech-to-text programs keep up with 150–200 wpm speech though.