Why is it that the schoolies usually stay around longer than the bigger bass? Is it because they can sustain colder water better, bigger bass need more food and can find it going south, would be interested in your thoughts.

Yep and yep... Smaller schoolies also don't have the urge / ability to spawn. It's a migration, much like with all walks (and crawls/flights/swims) of life...

I'd recommend for winter reading: Nick Kara's The Striped Bass. It digs deep into a lot of the biological and historical aspects of these fish.