Paracelsus:
<font face="Verdana, Arial" size="2">For example, how do you properly weight toughness compared to wear resistance?</font>
Toughness is a "step function", in that as long as a steel has the required toughness so as to resist fracture no more is gained by increasing it. So for example if you have a blade in D2 at 58/60 RC with a geometry that has the performance you like, and you have never had a problem with it, you would gain no performance increase from switching to A2 at 60 RC, because the toughness gain would not make a functional difference. However, wear resistance is not a step function and thus any gains in that area will translate to better performance (machinability is as well), as long as it is the failure point.
That is of course how a user will look at it, a maker can have many different perspectives. For example they have to consider the availability of the steel in the stock size they are working with. Does their furnace have the ability to work with the temperatures required for the steel (high speed steels demand very high hardening temperatures for example)? How is the machinability? As well, you have to consider trends and such, popular steels of lower performance could easily make more profit.
Anyway, as for steel comparisions, yes they can be directly made and they are in the references I have given above where you will see exactly such rankings. In the Bryson book he has the AIM selector which does this very well for a wide range of steels (not stainless). Anyone wanting a good overview of that would be well served by getting a copy of that book, or the Crucible text which has even more information in both numerical and pictorial representation. Materials texts have even more information but they are more complicated and are often not exactly in the form you would want.
As an example of such a ranking, compare D2 and A2. At at similar hardness level, 58/60, with a similar quality of heat treat, A2 will have a significantly greater impact toughness, D2 will have a greater wear resistance and corrosion resistance. D2 will also see a greater change due to cryogenics. You can put numbers on all of these and thus list them quite objectively. Now it is true that geometry plays an important part in knife performance (even where you buy the steel from can also), and as well that geometry changes can even make the performance difference so large that it swamps out the materials aspects. However all this means is that you have to consider both.
-Cliff
