My oldest falls into Dr. Ruf's level 4 based on milestones. The one time she was IQ tested was at age 7 and she was coming off a really poor school year and kind of shut down. She completely refused to complete some of the tests so her scores were all over the place ranging from the 25th percentile to beyond the 99.9th even within subtests. I say that as a caveat b/c that one set of composite IQ scores, while still gifted, don't quite fall into Dr. Ruf's level 4 range I think (I haven't looked @ the IQs for those ranges in a long time).
I would never venture to guess exactly the educational trajectory for a child based on IQ alone and I'm sure that it varies from kid to kid even kids with similar profiles. That said, the best advice we were given was to look at what was best for the child right now (i.e. - take it a year at a time and try not to worry about whether doing something like skipping a grade is going to be a bad move down the line).
My dd's trajectory has been to start as one of the youngest (just made the cut-off by two weeks - so on the other side of that than your dd), skip 5th, and subject accelerate in high school in her major interest area.
Assuming a kid with passion and no major twice exceptionality, I'd say that it would be safe to assume that a HG+ child will likely need alternations to the typical GT offerings especially if the school mainly offers in class groupings or limited pull outs. We've generally found subject and grade acceleration to be better fits than GT or honors classes (although I'd certainly take advantage of any honors/GT classes that are offered).
