R7800 SQM settings keep causing bufferbloat

Yes, you did.
I wrote "/sys/devices/system/cpu/cpufreq/ondemand/up_threshold" and
you tried "/sys/devices/system/cpu/cpufreq/performance/up_threshold"

There is no up_threshold in the performance governor, as it is always maxed out.

There is that parameter for the ondemand governor (where CPU speed varies according to the load).

I provided two alternatives:

  • use the performance governor (which you have now figured out),
    echo performance > /sys/devices/system/cpu/cpufreq/policy0/scaling_governor
    or
  • tweak the parameters for the ondemand governor to modify its behaviour to be more eager to max out the CPU.
    echo 35 > /sys/devices/system/cpu/cpufreq/ondemand/up_threshold
    ...

ondemand has several parameters that were also mentioned/discussed in those threads.

root@router1:~# ls /sys/devices/system/cpu/cpufreq/ondemand/
ignore_nice_load      powersave_bias        sampling_rate
io_is_busy            sampling_down_factor  up_threshold

more info at https://www.kernel.org/doc/Documentation/cpu-freq/governors.txt