Ha, @KGT... we really should have coffee sometime.
Lightweights Gen 3, are in fact stiffer, but so what. I tested them out thoroughly back to back once by setting my brake pads closer to the rim than I normally would then riding the hell out of them to see where I needed the pads set before no brake rub was evident. Before someone chimes in with a definition of what "wheel stiffness" really is, for purposes of my test lets just say I wanted to see which wheels produced brake rub easier. When I found that spot, I put the Boras on (the pre 2015 Boras), with the pads still adjusted for the Lightweights. I had to relax the brake pad spacing further in order for the Boras not to rub. Ok, I thought, so what... because after all my comparison testing I preferred the overall feel of the Boras, and I'm a bigger guy. I haven't done a similar test with the new 2015+ Boras, but it doesn't really matter, as I'm sure the new Boras would fare even better, so I'm talking worse case scenario here regarding the Boras against the Lightweights.
Speaking of stability, the Lightweights are positively horrible in crosswinds on a descent. If someone says they're not, then they haven't experienced much in the way of crosswinds. My friend who actually owns them, asked me why I didn't tell him about that before he bought them. I might have had I known him as well as I do now, but at the time I wasn't about to contradict what he was being told by the "bike shop", not worth the hassle. So I just said, "What good would it have done", the guys at the bike shop were telling him they were the best wheels money can buy and, because my friend was equating price with "best", he bought them only to find out for himself how terrible they were on descents. Which is really the best way to find out in the end, albeit expensive.
As for weight, no argument there, but I've found, with wheels especially, you can get too light to the point they get sketchy. To Lightweight's credit, they do not seem to suffer from that kind of stability loss I'm talking about here, but more than make up for it with terrible crosswind stability.
What I really dislike about Lightweights, and this goes directly to braking performance is their inability to produce a consistently perfectly true rim, especially when compared to something like a Bora rim. On a rim braked bike, modulation is very closely related to 1) how smooth your whole braking system operates (no cable friction, smooth operating calipers, smooth lever operation), and 2) how true the rim is. However, it doesn't matter how smooth your braking system is if when you're feathering the brakes so that they're barely touching the rim, that out of true spot rubs harder on every revolution thus creating a pulsing effect, and that's exactly what it does. It is incredibly annoying, especially if it's wet out, because that high spot will shed the water first and then "grab" in that one spot before the rest of the rim, creating that "grabby" braking feeling. And if your brakes are grabby at all, then your ability to modulate them is really not there either. The fact they can't produce a consistently true rim is a consequence of their manufacturing process... I'm sure it is very difficult to do since they have to "get it exactly right" at the time they're bonding the spokes to insides of the flat rim surface. There's no chance to fine tune them afterwards or in the field.
And don't forget about having to send the wheel back for even a simple bearing replacement (at least the front). And because they are cartridge bearings, you can't "adjust" them, they need to be replaced. Ugh!
Lightweights are probably the narrowest wheelset out there these days, with the flattest rim profile as well. They need that flat profile to bond the spokes to, and also as straight a line to the hub as possible, hence it helps if they're very narrow. They must be scratching their heads wondering what to do now with all these "shaped" rim profiles since Lightweight's design does not really lend itself easily to working with anything but a flat narrow profile, unless they come up with a different way to bond the spokes securely, not to mention adding weight. If they did that, they may have to change their name from Lightweight, to NotSoLightweight.
Bottom line is that Lightweights best days in their current incarnation are behind them. Do they care, I don't know...
It's almost neither here nor there at this point. But they did look good on my C59 when I had them... actually, now that I look at this pic again, I never did like the convoluted spoke pattern or the thickness of the side profile of the spokes, which also contributes not insignificantly to the crosswind problem.
Sorry to rain on your Sunday @KGT... perhaps if we meet for coffee we should stick to discussing the aero benefits of nothing. We'd probably agree a lot more readily then.