There is no concrete answer to your question. The signs and symptoms of dyslexia tend differ from person to person. Each individual with the dyslexia will have a unique pattern of strengths and weaknesses. Individuals with dyslexia generally have an inability to translate sound from their written form into their spoken form. This has a major impact on their reading speed and will vary between each individual with dyslexia. Reading speed is contingent upon the individual’s way of learning to translate sounds. Studies have shown students who have dyslexia are unable to read words much faster when they read a second time. A faster reader can read a ten-word sentence before a dyslexic person can read ten letters of the alphabet. Therefore, the average reading speed of the individuals with dyslexia in this study was substantially slower at reading a ten-word sentence than the non-dyslexic students.
Just like any kind of disability, dyslexia exists on a broad scale that ranges greatly from person to person. Dyslexia is a specific type of Language Based Learning Disability, that affects the ability for those who have it to accurately read and spell words. One of the largest struggles for people who have Dyslexia is decoding words. Decoding is the ability for people to take the knowledge of what letters look and sound like and to apply it to the pronunciation of complete words. Once students with dyslexia learn decoding strategies, they can increase their reading speed with repetition and practice. Knowing this, reading speed is dependent on the severity of Dyslexia, and where the student is in their remediation.
Also just a side note, though reading and decoding words may present an increased level of difficulty for those affected by Dyslexia, it does not hinder their intelligence.
Resources for further information: International Dyslexia Association