Well that's a new one for me. I hadn't seen that idea. The standard amount of GO is 30,000 units although in that other thread Jon suggest 40,000 for recent batches of Canson Baryta. I wonder how you control the amount of GO using this approach? My limited understanding of calibration mode (I'm on Windows, but it should be the same) is that it doesn't use any curves and if you wanted to control how much GO / ink is put down then you use the ink calibration slider, but how do you set this to get 30K or 40K units of GO?
There is a possibility that your problem is that you're putting down too much GO. I saw the linearisation plots from another user who had put down too much GO and while I don't recall exactly, I think it produced results like yours. Before you pay for a new profile I'd be inclined to repeat the exercise but printing GO the conventional way.
The conventional way to print GO is to print a 1" square white image and QTR automatically expands it to cover the printable area of the page. The variation on this that controls where you print GO is to have a TIFF that matches the printable area of the page exactly. This is harder than you think. You need to allow for the 1/8" non-printable border and not a pixel more. I could send you my A4 version but I assume you're on Letter. Then where you want GO printed you have white and elsewhere you have black. It's a little tedious to set up, esp locating the white rectangle exactly, by which I mean allowing for the 1/8" border. But it works.
If you still end up with a linearisation plot like the last ones, I'd consider them candidates for my Photoshop curves approach, given that they're not extreme and that they're relatively smooth. But I have a hunch that some of your problem may be excess GO. If you plump for a custom curve, make sure you print it with the amount of GO that you intend to use in practice.