I don't think Magnacut would excel with cardboard cutting.
You want 15v. It doesn't just keep an edge forever, the sharpening has been a pleasant surprise. The BBB heat treat is truly impressive (edit: Spyderco HT on the 15v may actually outperform the Spyderco HT on Maxamet, but you can check with the cut-tests referenced below). Maxamet is also a fine choice, and I have had no issue with K390 (one of my favorites, actually). For sharpening any of these steels, you will need CBN or diamond, regardless.
If stainless is needed, s110v or s90v. S90v is more well-rounded in my view, but less stainless.
You can check Outpost 76's youtube channel for some real world cardboard cutting tests. Pete, from Cedric and Ada cuts rope, which may be a good proxy. These are not absolutely scientific tests, in that not all variables are exactly controlled, but they will definitely give you an idea.
[Another edit: Manix 2 (and some others) may have a little better profile for cardboard, but the para 2 is an excellent knife. Should be no issue.]