It seems to me the older the child gets the less useful MAP is. I couldn't agree with you more that standardized test certainly doesn't equate to success in a class. An example my daughter was in a Algebra 2 class in eighth grade with kids that were 99% MAP scores. She's going into tenth grade now an now some are taking Calc BC, Calc AB and Trig/Calc A this upcoming year. My point is a MAP at this point is meaningless.
I think that MAP scores become fairly meaningless for gifted kids somewhere in middle elementary.