I've been eagerly following the thread to see what cables were working for folks at lengths over 30' as I've been struggling to get a true 4:4:4 4k60 passed from my PC to my two Samsung 4k TVs via my Denon AVR-X4200W receiver.
Like most, I had no issue getting 4:2:0 4k60 passed with my existing cables (which were all pretty new), but the full 4:4:4 was just not happening over anything more than 15'. Today I received a variety of cables and lengths to test out, along with a Monoprice Blackbird repeater. Here's what happened:
Tested new 30' Monoprice Cabernet active HDMI cable directly from PC to TV = working at full 4:4:4 4k60! Plugged the cabernet into HDMI out 1, plugged PC into Denon with Cable Matters slim 6' HDMI = max 4:2:0 (no 4:4:4). Proceeded to add a 6' HDMI before the 30' MP Cabernet and joined with BB repeater = no 4:4:4. So while the 30' would work directly from PC to TV, I cannot get it to play nice when mixed with the receiver.
I then tested two 15' KabelDirekt HDMI cables, connected with the MP Blackbird repeater and plugged into the HDMI 1 out on the receiver. This was a success, pushing the full 4:4:4 4k60 down the 30' cable to the TV (while also feeding the same signal from the receiver's HDMI 2 to my other TV/monitor down another 15' KabelDirekt HDMI). I did have to swap out the PC HMDI cable from the slim Cable Matters to a 6' KabelDirekt with this setup. While the older, Cable Matters cable does work for the second monitor, which is only on a 15' run, it would not work with the longer run.
My take is that there is a pretty hard stop at 15 feet for full 4:4:4, or at least has been my experience. I know others are reporting success on longer runs, but all my testing seems to hit the wall if I go over 15' (and that includes Source to Receiver cable lengths included in the overall calculation), where things start to get really finicky.
Hopefully the 15'->BB repeater->15' setup will continue to work (will test for a week or two before I go pulling cables again), but that seems to be the only way I can get things working properly.
A question for the group: what source material actually plays at 4:4:4? My research seems to indicate that Blu-ray and UHD BD only do 4:2:0, and while my PC's GPU does full 4:4:4, it appears that consumer grade GPUs are limited to only 8bpc (I hear the Titan does 10bpc+, but not my GTX1080), so I don't know of a way to test full 4:4:4 10bpc with any gear. Likewise, the Xbox One S does only 4:2:0 and 10bpc (which was interesting since I was getting partial success with the Xbox One S when testing 4k, but that seems to be due to it not being 4:4:4. I see mention about the Opposite UHD-203 doing 4:4:4, but for what purpose (since UHD is only 4:2:0)?? Am I missing something? Are we all chasing a resolution that, frankly, just doesn't exist in source material?