I'm not 100% sure but I think many graphs compare the steels at their optimum RC for their desired applications. S7 is used for Jack hammers so you don't want them at too high an RC or they would be brittle and crack.Dan probably runs it at a little higher RC so you lose a little toughness but gain on the edge holding.You often hear of some 'super steels' keeping an edge seemingly forever but you often find they are quite brittle and would never survive what a Scrapyard blade can.Years ago Nessmuk etc liked to have a lower RC knife so that they were easier to sharpen.