Hope the IM vet visit provided some useful information.
Sadly, there is no current test for GH output in cats, so not something that can currently be tested.
Too much insulin does NOT seem like not enough, provided you are doing safe size increases and testing enough to know how low the dose is taking the cat. The only occasions this might happen is when someone starts on too high a dose, or doesn't test enough, or increases by too large an amount. None of those are present in Eddie's case.
I think you can safely say that Eddie has lost his blues and could use an increase.