Hello ReverendAndy!
Sounds like a great cruise. I thought I'd throw out a random thought or two and perhaps get back to this thread when I get a little more time and/or if you are interested.
You mention Oaxen and Mathias Dahlgren but if you're toying with blowing the bank (and are extremely lucky with reservations), you might not want to forget Noma in Copenhagen.
I can't vouch for the dollar/enjoyment ratio of either Oaxen or Mathias Dahlgren but both are supposed to be truly exceptional. Mathias Dahlgren actually has two restaurants at the Grand Hotel: Matsalen ("the dining room") and Matbaren ("the food bar"). Matsalen is 2 starred and I've seen nothing but outstanding reviews since they opened. There is no on-line menu as chef Dahlgren is meticulous about choosing market-fresh ingredients. Very Swedish, very hip, very expensive. Matbaren is slightly cheaper and a little more relaxed. I'm itching to try Matbaren for a long lunch one of these days and your inquiry may be enough to get me over there before the 1st of July. If I do get there, I'll let you know. All booking/contact info for Matsalen/Matbaren is online.
Oaxen is actually situated a good bit south of Stockholm so you'll need to add the cost of a pricey (100 dollar plus, one-way) taxi into the equation. They also offer lodging but I doubt you'd be intersted as you'll have your boat in the heart of Stockholm during this time. Despite the difficulty of reaching Oaxen, it is also supposed to be spectacular. Oaxen also has
an excellent online site.
I've got a few other Stockholm posts on the board but I'll still recommend Operabaren and/or Bakfikan (both restaurants, along with a third - Operakällaren - are located in Stockholm's Opera. Much less expensive but still good Swedish food.
Is the boat by any chance stopping at Visby, Gotland on it's way east?