I'll do some digging for you later on #2 and see if I can come back with more info. In re to #1, it depends on the child. The SB5 has the reputation of being a good test (in terms of showing the kid in his/her best light/getting higher #s) for mathematically inclined kids who are penalized by the speed aspect of the WISC -- probably not so much so for verbally gifted kids who are penalized by timed aspects of the WISC.
My oldest had a FSIQ in the upper 120s on the WISC IV due to the processing speed subtest (in the 42nd percentile for her) and a GAI in the 130s, like your son. On the SB5 (which she probably didn't do her best on due to nerves), her overall score was very similar to her FSIQ on the WISC. Reading, science, and language are her strongest areas as well. She's tested btwn 4-16 grades above her current level in all areas of language (writing, spelling, reading) since she was in 2nd grade. As a 6th grader now, the school tests for reading top out around 12th, which she hit in 4th, so I don't know "how" advanced she is there now. Anecdotally, the SB wasn't necessarily a better test for dd#1 despite the lack of time penalties.
How was his working memory score on the WISC? I think that part of it may be that dd's working memory score was very high on the WISC, so her FSIQ was still pretty near gifted even with the speed part dragging it down. The SB5 has more of a visual memory subtest rather than an auditory memory subtest, so that may or may not be better for your son in that part.
