Before looking at that chart, I thought that C2 was inferior to C3, which was inferior to C4. In other words, the higher the digit, the better the carbide. Now I am no longer sure. It may more subtle than that, where you must balance hardness, brittleness, etc.
Working in a custom tool and die shop for 40 years and have seen the progression of carbide and carbide choices over the years. In an industrial setting minor details in carbide makeup, can and will, have dramatic effects on production,,,,,,, when in an extremely controlled environment.
This means day in and day out the material being cut remains the same, the depth of cut remains the same the feed rate remains the same, etc. Unless those variables remain the same, the difference in carbide performance will be difficult to quantify.
When viewed under a high power microscope, all cutting edges will show a cutting edge which is made up of many many small teeth. The size and depth of the gaps in those teeth, is a result of both the sharpening method and the grain structure of the material which makes up that edge, in this case, carbide.
We could purchase carbide, either a "ground and lapped" or just a "ground" edge. This of course addresses the sharpening method.
Or we could purchase a lower priced carbide, verses a "submicron" grain structure at a higher cost. This address the affect of grain structure in regards to the "teeth" produced when grinding a cutting edge.
For the hobbyist wood worker, I would suggest looking for a product with claims of "sub-micron" grain structure within the carbide. A router bit company, using a "better" (sub-micron) grade of carbide, most likely may
use a "better" sharpening process as well. (who knows for sure?)