If it's any consolation I'd be way too curious to not try the WISC. I'd just have to know, especially since it isn't unheard of to test lower on the OLSAT.
I have a friend who's kid came out PG when they screened all of the kindergarten kids in the system. They were completely blind-sided and the kid showed no outward signs of being gifted (to the parents or teachers). Even now meeting the kid he seems very average (I coach and volunteer a lot with kids). Not all kids are super obvious and with a gifted sibling I wouldn't want to miss a hidden talent (and/or LD masking it) just because I didn't look. That and I'm just way too curious
