Well, you need to consider what Keith Stanovich calls the Matthew Effect. If you're not reading well or easily, then you have less access to the curriculum (whether that be formal curriculum or just the stuff floating by in your life). So you learn less from what's around than other kids are learning, both in terms of content and in terms of learning strategies. So you have less fund of general knowledge, less experience solving complex problems, less experience self-regulating as a learner. This becomes a self-stoking cycle -- the less you read, the less you learn, the less you read, and so on. The poor reader will tend to diverge more and more from the normal-reader population over time.
Similarly, there's a reverse Matthew Effect with gifted kids -- they get better and better at extracting more and more information and ideas and strategies from the world around them, they learn more and more, and so on.
So it's not unreasonable to wonder if a GT kid who has chronically been struggling to read might start to lose ground compared to those who have not had to try so hard.
In terms of techniques that are helpful for dyslexics, the key words are multisensory, structured, sequential, phonics-based. There is a whole chart comparing the various research-supported intervention systems on
http://www.interdys.org/ewebeditpro5/upload/MSL2007finalR1.pdf
