We have similar/even larger spreads with DS7 between his PRI (instead of VCI) and his WM & PS. It has affected the way I homeschool him because it DEFINITELY affects the way he works. He needs to write things down because his memory can get in his way, he needs time to think things over, and we have to work on memory and processing speed to try to improve them, just as we would any other weakness.
So does a spread matter? Yes, I think it does, assuming the test scores reflect what you see of your child IRL and aren't some sort of testing anomaly. I believe that my son really does have a PRI that's amazingly high and that he has a much more average memory and processing speed. That reflects what I see.
What does that mean? Well, for us for now, it means that homeschooling with me is a good educational choice for him, as is working with teachers who allow him time to think and allow him to write things down. Someone who thinks fast=smart is not for DS7, as we've learned the hard way...
However, that doesn't mean that having that high PRI or VCI is a problem, and I do NOT think there is an "optimal IQ for a successful life," unless by that the speaker meant "fitting in."
Fitting into a system as it stands and having a successful life are two very different things! Often the people commonly called the most successful don't even begin to fit in. And they are often extremely smart people.
This sounds like a valorizing of the social over the intellectual to me, FWIW...
