Please see the link below for oral fluency reading statistics based on WCPM (word correct per minute). This will give you an idea of how fast your child reads in comparison to other children.
I have a very fast reader too. She had comprehension problems at first, but it was more due to age and maturity more than anything else. She could pronounce words perfectly with no idea what they meant in addition to having problems associating reading with how the real world worked at times.
She does not like writing very much either. Her gross and fine motor skills were the last thing to develop, so that may be part of it.
(This is the same kid who lost over 100 grade points last year because she did not put her name on her paper. In addition, she would habitually leave the punctuation off the last sentence on almost every paper because she wanted the assignment off her desk as soon as possible!)
http://www.readnaturally.com/pdf/oralreadingfluency.pdf
