I find the DMT suggestions a bit generous in advancement, so I'm not sure I'd extend them fully to the other subjects. Each subtest has a different mean and range of scores too, so a high science score is much more common than a high math score.
English mostly tests grammar and sentence structure. It doesn't follow, for me, that a student who recognizes poor structure in a multiple-choice format can write very well when asked. If the score matching writing, then acceleration would make more sense.
Science doesn't really test science knowledge, but rather science reasoning -- whether a child can interpret a graph, understand what an experiment would test for, etc. Scoring well there doesn't mean that a child is ready for high school science if you think that there is meaningful content in middle school science. I never thought there was meaningful science content in middle school since my child read science texts all the time and had self-taught anything relevant already.
And for reading, scoring well indicates a level of close reading and vocabulary that seems more like math to me. Once you've got good skills in inferencing, understanding point-of-view, high-level vocabulary, etc., then I'm not sure what benefit 5th or 6th grade literacy would provide. There are always more books to read, but it is much more satisfying to have higher level concepts for someone capable of higher level thought and appreciating subtlety.
