There was a recent discussion about what/ how much to tell that might be of interest:
http://giftedissues.davidsongifted....t_to_share_with_DS_regar.html#Post208379An additional thought to add to that thread: one of the big challenges in identifying problems and understanding the impact of disabilities is that the kids don't know that other people see/ hear/ perceive/ read/ whatever differently, so they don't tell us when something is wrong. How would they know? So by sharing with your son how stealth dyslexia may impact reading and writing, you are giving him the tools to recognize himself what "ought" to be happening, and to be able to tell you when his experience is otherwise.
I am still up to my eyeballs in Shaywitz, Eides and everything else I can get my hands on. One message coming through clearly is that a stealth dyslexic is still dyslexic, and that reading with "the wrong" part of your brain is demanding and exhausting in ways that using the "correct" part of your brain isn't. I am slowly starting to appreciate the toll that heavily compensated dyslexia has probably taken on several family members, very successful people in whom dyslexia has never been suspected - until we started opening up this conversation and are realizing the extra price they have been paying, every day, all their lives, to succeed as they do. For your son, for reading to be a strength despite the likely presence of dyslexia is an enormous affirmation of his abilities, not of a disability. This alone could send him a powerful message about his ability to overcome other challenges.
And can I second Percy Jackson? My dyslexic/ ADHD-I DD8 continues to proudly embrace her demigod status - to the point where last week, on discovering her eyes did not track or converge together (thus adding visual processing to our diagnosis list), she informed me most seriously: "But Mommy, demi-gods need to be able to pay attention to a whole bunch of things at once, so maybe our eyes are *supposed* to be looking at different things!"