Paracelsus :
Most serious wood carvers I know are not fond of any of the diamond stones. They take off too much metal too fast and do not produce a fine enough edge for push cutting through very hard woods.
Yes, even the u-fine diamond grit, is still far rougher than optimal for push cutting. The abrasives I mentioned however are far finer, and will sharpen the edge geometry I mentioned very quickly. For normal work you use the CrO 4-5 times and then go back to the 5 micron SiC once that stops being productive and then back to the CrO.
In regards to grain sizes and fine edges, the CPM grades, at a very high hardness, and with a full cryo treatment, will have a very fine grain, easily better than all but a few of the conventional steels, the only thing better will be something very simple like 52100. The grain size of 10V for example is only 2-4 microns, far smaller than you might think given its alloy content.
In regards to stainless in general, no I would not use it in a whittler as there is no real advantage, however it I had to, 420V would be where I would go. In general the "ease of sharpening" issue is far more dependent on geometry than steel, and with the proper geometry and abrasive, it is just a matter of a few passes, since the steel will see little to no degredation.
Now if you stick to natural abrasives and work with high alloy very hard steels, sharpening will be problematic, but there is no reason to do so. I do agree that the benefits of ultra-high alloys are going to be minimal as you can't really refine the existing edge geometry as its pretty much optimal even with simple steels, and upkeep with those is just a routine few stropping passes.
Wood comes into play as well, there are some really abrasive hardwoods, I have not carved any amount of them though.
-Cliff