The Kindle voice CAN be sped up, although I too find the highest speed just a little too slow too. The male voice seems better than the frmale and the enunciation isn't all htat bad (despite my complaints in another post).
I do wish it could be sped up a tad more and maybe underline the word that is being read too.
I too am dyslexic and really appreciate my Kindle DX's read-to-me feature. I hope Amazon does not cow-tow to the publishers and remove it.
Remember , it's not lisdexic to be easy