Okay, did my first real ride today and can provide some impressions.
Let me start with giving my frame of reference for comparison - I've been riding only DA 7900-24 tubeless wheels with Maxxis tires at about 90F / 95R for the last 18 months, nice solid wheelset. These new wheels are built from Farsports ultralight 38mm rims (20.5mm wide), Novatec SL hubs 20/24 spokes (1263 grams total weight) with Veloflex Corsa 23s on them inflated to 110F / 115R for this ride. Also installed SwissStop Black Prince brake pads. I go about 185 lbs after a relatively sedentary winter. Not a racer but not a total slug, BB category recreational rider who did 3K miles last year. This was just a break-in ride doing about 36 miles on a MUT in Northern Virginia, so no rough roads or steep hills requiring much braking were experienced yet. Temps in the 50s, sunny day with quartering/side winds all the way.
General impressions, they spin up / accelerate quickly and hold speed well on flats. Maintaining speed on rolling hills, and pushing it on the uphills, I was rewarded for the effort . No wheel "chatter" or extraneous noises noticed, but I had my ears partially covered, so a closer look at that aspect later. Didn't rub the wheels on brakes or frames even one time, no matter how much I was jerking the bike back and forth while pulling / pedaling hard. So, plenty "stiff" and very comfortable (although I'll play around with tire pressure a bit). Hub noise minimal and not annoying, but I had a little extra grease added during the build, and quieter is my preference. Braking was really nice, firm and smooth, comparable to or perhaps even better than the D-A alloys, but I didn't do any long or steep downhills, and real hard braking was done only a couple of times to test effectiveness and braking noise.
For purposes of Just Riding Along, there's no real performance improvement between the DA C24s and these new wheels. In fact, it's hard to beat that tubeless set up for all around comfort and sense of reliability.
Pushing hard is where I noticed the difference with the new wheels. At a higher level of exertion, they just felt faster in each aspect, and my efforts were rewarded. Probably some placebo effect involved, and it isn't a huge improvement or one that could be quantified, but is to be expected simply based on reducing overall rolling weight in wheels and tires by about 250 grams. These are just first impressions, and I'll report more as I put on the miles.
p.s. They look cool too.
2011 Tarmac Pro SL3 Project Black (gone but not forgotten)
2012 Parlee Z5 SLi (just because)
2014 Colnago C59 (why not)