I agree that a lower brittleness is more important than edgeholding in a knife you only use once, but has a thin tip. However, ATS-55 has neither exceptional strength nor exceptional corrosion resistance nor exceptional edgeholding abilities, in my experience. It therefore seems reasonable that spyderco, who happens to be the sole producer of what is probably the best defensive knife design availible, should make that knife with materials which will bring out the full strengths of the design. I suggested CPM440V because at slightly lower than perfect rockwell, it still holds an edge better than alot of stuff, is still strong enough not to break, and is very corrosion resistant.