Welcome, geggie!
In general, you may find value in the GAI if the lower scores are concentrated in the relevant WM (digit span) or PS (coding) subtests, only, and not in any of the VC, VS, or FR subtests. If at least one of those two subtests is not markedly lower than the other subtests, then you will probably not see a meaningful difference between the FSIQ and GAI.
Also, the value of the GAI depends on whether it changes your understanding of your child's learning profile, and whether it changes access to resources. If either of these is the case, and if you care to share a bit about the profile, I may be able to give you an idea of whether it's likely to be worth pursuing the GAI.
