So here is another update:
Received the Stelvio shock. It has indeed been upgraded with a Hyperpro spring. The spring reads "hyperpro 91323" which is followed by either 0522 or 0552, can't remember now. I've been unable to find any real specs on that spring.
A generic motorcycle workshop nearby swapped the shocks for me, as I was too busy and would have had to borrow some tools. It took the guy a little over an hour to swap the shocks.
I haven't done anything to properly setup the shock at the moment. I will need to dial in the preload for riding by myself as well as with a pillion. I cannot reach the compression dial any more, its hiding behind the tuning fork now.
First riding impression is really good already. Steering feels good, and I'm quite impressed with the smoothing out of the bumps. I think a lot of the improvement "out-of-the-box" is the feeling of a progressive spring. This is my first one, but it feels like it's smoother for small bumps, and firmer for bigger bumps. I will have to get used to it.
Thanks everyone for informing me in earlier replies.