Update on my testing of various cables to find some combination that would go 25ft.
Monoprice 20 ft Certified Premium worked great at 2160p60 RGB 444 but too short to be useful. 20ft is the longest cable they make.
Adding a passive female-female connector and a 3ft CP cable introduced some sparkles on black background and very occasional white flashes. (20ft CP + connector + 3ft CP)
Belden BJC Series-1 25ft worked great. What a monster and no problems at all running RGB 444 2160p60 over that length.
Adding a passive female-female connector and a 3ft Certified Premium HDMI from Monoprice also worked fine (25ft BJC + connector + 3ft CP).
Adding a passive female-female connector and a 6ft Certfied Premium HDMI from Monoprice worked but with obvious sparkles noticeable around text when the PS4 switched to dark mode (after a timeout the screen darkens somewhat, no problems seen on a normal screen).
Same as above but using a Belden FE series 4ft Certified cable failed with constant white flashing of half the screen.
Inserting the 4K Blackbird anywhere in the chain with any of these cables failed to even show a screen, with the HDMI constantly trying to resync. As a test I inserted it between two three foot cables going from the PS4 and the receiver and that worked, so the unit itself was working it just isn't good enough to handle a 20ft run between the source and the input to the Blackbird. I also tried a 3ft CP cable to the Blackbird and then to the BJC series-1 and that didn't work either.
The BJC Series-1 is the best cable out there and has no trouble running RGB 444 2160p60 over 25ft.
The Monoprice Certified Premium cables are pretty damn good and by far the best value for money. Max run length though is 20ft.
Belden FE series was disappointing. Not as good as the Monoprice cables and a lot more expensive.
Monoprice Blackbird. Waste of time, got better results with a simple passive connector than with their active repeater.
Since I really need at least 4ft from the connector to the TV using a connector isn't an option so it's going to be one 25ft run connecting directly at both ends.