I wrote this earlier but I lost connection...
It might be a good idea to look at even modern high-performance "traditional-style" swords being made. Some features you may notice is that they tend to be rather thin compared to older pieces, and many pieces have somewhat flatter cross-sections. This often makes for light, fast swords that have very crisp edges and can more easily cut targets like tatami-omote.
This brings up the old question of what characteristics make a good sword. The most specific answer would be that swords and expectations of them are shaped within cultural contexts, but let's expand this into a broad sense...I'll list a few simplified things that I think make for a good sword off the top of my head, but the list may be far from complete. In no particular order:
Weight: A good sword must have sufficient substance to make it more than a sharp feather. At the same time, it must be of reasonable weight to be comfortable to use. It is benefitted further with balance.
Balance: A good sword needs correct weight distribution. If the center of gravity is too far out, it will cause you wrist strain over long periods of time. It will not be comfortable to use. If the balance is too far in, the blade will feel too insubstantial and lack any power, while the handle will contain most all of the heft and feel awkward.
Handle Ergonomics: The handle is more than a "stick" that you use to hold onto the sword. It should be comfortable for the user. It should lend itself to changing positions when applicable, and not lock the fingers into certain spots, which may become uncomfortable in different stances or cuts.
Blade Shape/Cross section: The shape of a good sword will allow it to cut well, while offering sufficient strength and rigidity to the piece. Depending on your sword style and the intended usage, this will vary. It is also one of the more complex aspects of the sword.
Flexibility: Optimally, no sword should break until an extreme amount of force is applied to it. To avoid breakage, a good number of old swords were more than willing to bend like taffy. However, excellent blades of all time periods would resist bending to a good degree. The way some talk, it would sound as if this is the only real measure of performance.
Edge Retention: Some may not feel that a very sharp edge is important. However, a good sword should cut well because it has an edge capable of cutting, not because it has a mild edge and enough weight to push it through. Thrusting swords might not benefit from a sharp edge quite as much, but I believe it is helpful all the same. I feel that many people underestimate the durability of a well made sharp edge with the right geometry--even for chopping. I think a real sword should take and hold a good edge, so I add edge retention to the list.
Harmonics: This topic has fluctuated in popularity, though I think most people understand the basics of it now. Good swords often use harmonic balancing to minimize vibration at the handle and at the sweet spot of the blade, so that cutting effectiveness is not hindered, nor will the grip quickly loosen because of vibration. This is an issue in some swords more than others.
Intangibles: Many people feel there are qualities that are not expressed merely through physical characteristics (feel, livelihood, spirit, etc). Some identify these as combinations of positive physical factors, but I will include them here to give credit to those who feel that way.
I'm sure there are more, so this list is not exhaustive in any way. However, would you say that factors such as these are common in identifying "high performance" swords of numerous styles? What are the main contributors to these characteristics? I would guess that design and heat treat are the most direct influences.
Steel is a funny topic. Many things said about steel come from the perspective of factory-made blades, or the results a few makers have had with particular steels. Makers who are capable of doing what they want can routinely make "exceptions" to the "rules" of what steels are good or bad, suitable or unsuitable. I use Jerry as an example, because he made/makes swords of 3v that are supposedly rather good (so I hear, I haven't held one in person
). There are people who make high quality 440C swords and still the sword community tends to dismiss it entirely! Could that be because those swords do not use traditional style or design? Possibly...
I'd like to see a quasi-traditional katana or other type of blade in 3V or other new steel for a lot of reasons, but a new one is just to show people that it can be done, and possibly work very well! Maybe in the future something like this will happen. However, its impact on the sword community would be questionable...sigh.
