For HG+ individuals without 2e, testing in middle-to-late childhood is actually best (8-12 yo), as there is still enough range in the tests to be able to use extended norms. Scores may be more stable in adulthood, but ceiling effects become more problematic for the highest-scoring individuals. (Not an issue if we're looking at <145.)
I think you're probably right when it comes to the 2e aspect, and I think that's what has influenced my opinion. I'm HG (153) w/o a diagnosed LD but could be ADHD like my son, and I feel like the time of my testing (via the SB, at 27 yrs) was the best in terms of stability (I think I would have tested more like my son as a kid - although my high scores would have been higher than his but I would have had behaviour related variability). As an adult, however, I'd kind of settled into my levels and was definitely more stable.
I don't know... there are pros and cons to each testing tool, like you say. Not only am I not sure that the WISC was right for my son, I also wonder about the suitability of the psychologist - she was very, very competent and experienced, but much too gentle. She was more suited to the anxiety-ridden kids as opposed to my hurricane kid... lol
