You have to be patient to see the effects of cabergoline. I've seen some cats react (lower dose) in a week, and some take a couple months. Sometimes you will see some of the acro side effects diminish as well. You will need to test frequently. Some of the cats have a very strong reaction to it and need a lot of frequent reduction. But there is no pattern to predict how Pumpkin will react. I have seen some reference to cabergoline working better based on some aspect of the pituitary tumour, based on imaging. Most people don't get imaging first - too expensive.
And as Suzanne says, retesting the IGF-1 won't tell you anything. There does seem to be an impact on growth hormone, which we cannot measure.
Cats that experience GI effects seem to benefit from going to every other day dosing. And yes, it's kept up for the life of the cat, but the frequency could be reduced.