I would have to disagree with you about the lower carbon content meaning lower edge holding capabilities. It can be true if you fully harden both of them in the same way, simply because more trapped carbon = more martensite. However, this also makes it more brittle, and increases the need for a longer and more thorough temper. A steel like 5160 has more than sufficient carbon to harden to or beyond RC 58, which is what many consider to be an ideal edge hardness. Of course with these steels you don't need to worry about carbide formation or anything of that nature, so we can keep it simpler.
Ultimately it winds down to the heat treat. Many treat it as a static process that yields static results (aka this steel is better than that steel), though I personally disagree with that line of thinking. However, a generic heat treat on 5160 is actually more forgiving to inaccurate timing and temperature than steels like the higher 10**.
Personally, I like 10** steels a lot when they're really clean, and I wish 5160 were more rare because I tend to like unique stuff the most.
But as is the case with most blades, it's not the steel but who does the work. I would say on the average, they're both good enough to use, but I tend to like the aesthetics of the mid-range Hanwei pieces more (though that doesn't say a whole lot). I especially like the fact they're dismountable. I would also hazard a guess that they hold a slightly better edge than the KC stuff also, likely due to the heat treat as a result of the sword's intention. Really, would you want a potentially chippable edge on a sword that your customers use for whacking brush and plywood targets? Maybe it's different now, but I'd like to hear new KC stories and see new KC blades, so we can change that view if necessary.
KC got a lot of extra attention in the last few years particularly from SFI. I don't know if the attention was really deserved, or people were just desperate to see the Hanwei empire lose some of its ground to an underdog like KC (sorta like how some computer geeks want to push non-microsoft operating systems).
Unless you get a lemon, either manufacturer makes a good "quality" blade, assuming we let the aesthetic pleasantries slide. I much prefer the looks of the Hanwei models, though I think with a lot of work, either sword would make a great project.
