I wouldn't sweat a point or two at this age. I think you can reasonably say he is somewhere in the ballpark of MG. Working memory is important (especially to math) but it's certainly not impossible to be functionally GT (even in math) with not-exceptional working memory. Happens pretty often, actually. And at this age, attention and motivation are fairly significant factors in working memory (and other) performance. The average Similarities score may or may not be meaningful. Again, he's young, and lots of other factors besides actual raw cognition affect performance.
Bottom line is, he's very young, so unless there are functional indicators that align with his specific test profile of strengths and weaknesses, I wouldn't invest too much energy in interpreting it. If one label or another is important for access to resources that other aspects of his presentation make clear are necessary, or if there are functional IRL concerns or problems that need to be teased out, that's a different scenario, and perhaps you wait a few years and re-test with the WISC. But he's a bright kiddo! I can't imagine one point was going to make you parent him differently.
