
I managed 6.795 kg (and that's with approx. 70 g of RideWrap), largely with the help of a 140 g cassette from ZTTO (SLR Gen 3). I purchased it from ZTTO's AE store, after it told me that the Gen 3 was engineered to have smoother shifting over the Gen 2.
The cassette was stupid light, but my shifting became
absolute garbage (Ultegra R8000 groupset with KMC chain). I and two other bike shops continually adjusted the derailleurs and shift cable tension, but it continued to skip gears, not get into the highest/lowest cog, and announce to at least one street block that I was riding by.
I switched back to the Ultegra cassette and the calm after the storm was life-changing. Before I give up on aftermarket cassettes altogether, I thought I'd get your feedback on any positive experience you've had with particular makes/models of lightweight cassettes.
On another note, I'm swearing off ZTTO forever. Besides this cassette, I had purchased some handlebar tape that quickly disintegrated after a mere 2,000 km of fair weather (all sun; no rain) riding.