@LosGatos
You certainly mean 55 Hrc. I don't even know if it's really possible to have a steel 65Hrc, and if it is, glass seems tough in comparison. I quenched pliers (not tempered, and certainly with a high level of carbon) just for fun, and it broke in the thickest part the first time i tried to cut a 3mm brass rod.
Anyway, here is the description CS give of the SK5
"SK-5 is the Japanese equivalent of American 1080, a high carbon steel with carbon between 0.75%-0.85% and 0.60%-0.90% manganese. As quenched, it has a hardness near Rc 65 and produces a mixture of carbon rich martensite with some small un-dissolved carbides. The excess carbide increases abrasion resistance and allows the steel to achieve an ideal balance of very good blade toughness with superior edge holding ability. Due to these characteristics, this grade of steel has been used traditionally for making a variety of hand tools, including chisels and woodcutting saws, and has stood the test of time and use over many years in many countries."
(note the "near 65rc", which means "63-64Hrc but we have a bigger one", and no one cares about the hardness just after quenching, it is brittle as glass, it's after tempering what matters)
I can't find a precise steel chart for the carbon V, as it is only a commercial name used by CS. They don't seems to communicate much about the steels they're using. Anyway, it seem's to be a 1095 with added chromium and nickel, plus a bit of vanadium.
They could be realtively close in performance. I never tested any of these, so i can't tell by experience. But remember, the composition of the steel is only a part of the final performance of a blade, the heat treatment is as much important, but it's something we can judge about only by testing. A lower carbon, cheaper steel, but treated perfectly can finally have better performances then a modern one quenched too hot, tempered too hot and too fast.
