I may be wrong, but I think Jackson Ultima has also sold 420 and 440 steel alloy blades in the Matrix lines.
I don't know of anyone who has run the experiments you would like on ice skating blades on ice. I suspect the results would vary with the mineral content of the ice, as well as how good a job you do of drying the blade, how you store it, humidity, and the exact edge shape the sharpener produces. Maybe even on smog. (I know by experience that salt spray in the air near seashores affects stainless steel bolt rust on roof racks and truck caps.) Also on how much stress you put on your blades, and what types of stress. In other words, different people might get different results on how important the difference is between 420 and 440.
I can't imagine trying experiments on high end expensive blades, unless you have a bunch of ones that are too worn out to be used.
To add to the complexity of your question, this source
https://www.bladehq.com/cat--Steel-Types--332says that there is more than one type of 420, and more than one type of 440. (That source is talking about knives, not ice skates, which are used under very different environmental conditions than ice skating blades - so what it says about how long the edge lasts should be taken with a grain of salt.) On top of that, hardening also affects blade edge longevity, so there are a lot of variables.
Some of the new rental skates at work have been greased, though maybe that doesn't affect rust on the parts that touch the ice, because it rubs off. The sides of the blade feel a little sticky, and aren't quite as shiny as they would probably be without the grease, but the grease seems to be lasting a lot longer than the oils I have used.
Didn't you mention you have played with grease on blades? If so, what were the results, or didn't you feel like running experiments that could create rust on your expensive blades?
Be a bit cautious with Paramount. I have seen a Paramount blade that came apart during a jump landing. The lady said she had broken a bunch of them, by doing imperfect split jumps, which presumably created extra sheer stress. The ones I have seen (this was some time ago) were held together with adhesive, whereas the similar looking Ultima Matrix blades are held together with adhesive AND two screws. The screws add a tiny bit of extra weight, but it isn't clear it is a sufficient amount to matter. Of course, Paramount blade shapes are different than Matrix blade shapes, so longevity and weight aren't the only factors, as I'm sure you know.
With your technical bent, I bet you take good enough care with your blades that you don't need to worry about rust. Are you only worrying about durability?