My DD has a 70 point difference between some of her scores.
Her GAI is 170 (WISC extended norms) and her Processing Speed was bang on 100. I can't remember, off hand, the full scores though her GAI without ex-norms was 157.
For DD, she scored far higher GAI wise than we imagined as she always seemed to struggle to get an answer out, seemed to think for hours or just look blank.
Our Ed Psych suggested looking at ADHD so we went down that route.