I was looking to "equivalent" table, where is mentioned W1 up to 1.1% of carbon. There is so much tolerances in W1 specifiacations than we (in Czech Republic) make 3 or 4 different steels, which all should be W1 equivalent . . .

So SK-5 is something in the middle, but real difference is not marginal, for todays standard it is "not enough" for at least average knife.

BTW: All W1 equivalents we made was the worst or cheapest tool steels produced and it was in communist era, so it speaks for itself :-), D2 equivalent has much higher number in our norms . . .