Mike: About Nitrobe 77, it's reportedly hard to get and only in 2mm thick barstock. That seems to be too thin for a typical straight, maybe a frameback though. The nitrogen replaces the carbon and significantly improves rust proofing. For comparison, stainless steels will rust. One of the folks who tested this stuff ground the blade from hardened stock because heating it to heat treat it will drive off the nitrogen and lessen the desirable qualities of the nitrogen saturation. The heat treatment routine requires a cold quench/cycle four times. Hard to get, complex heat treatment, excess care grinding all equal expensive.
Joed: plain carbon (low alloy) steels that are correctly heat treated do not generally require nor improve from cryo treatments. In high alloy steels that contain aggressive carbide formers like chromium et al, there is retained austenite. Cryo treatment converts retained austenite to untempered martensite, so an additional tempering cycle is needed when this is done. Some steels will have retained austenite upwards of 25% despite cryo treatment and those would include most of the exotic alloys previously discussed in this thread.
Austenite is relatively softer than martensite. For most applications it is detrimental in the steel. In some steels retained austenite can convert over time to untempered martensite at room temperature. This is the basis for some legends about blades getting harder over time. This is probably best explained by increased brittleness from the untempered martensite formed from the RA because when this phenomena was noticed there were no really scientific methods of hardness testing and that metallurgy has improved the ability to microhardness testing and differentiate the martensite and the retained austenite.
The CPM, powder metallurgy metals are a big improvement because of the more even distribution of all the alloying components, but it's not the carbon equation. As soon as the steel is heated above austenitizing temperature, the carbon will go into solution and diffuse evenly throughout the bar no matter the particle size originally. If temperature controls are closely exercised CPM steels will have a much finer crystalline grain size than a cast steel type could get even with repetitive grain refinement cycles but then if you're like me and enjoy the appearance of dendritic carbides those are lost.
As always, there is a balance between features and performance. Some of those can approach each other around a mean value while others have to be balanced at both ends of a spectrum of effects.
Rsq: there is a phrase, the better is the enemy of the good. I don't believe you will find a perfect steel. In three to five years, your perfect steel will be ordinary and out of fashion and not cool any longer.
Even so, I admire all your enthusiasm and would not discourage you in your exploration. I remember when I was like that. Now I'm old and in the way. Happy too. :)