A processing speed of 20x means that Roon is able to process a file (Mqa unfold, sample rate conversion, parametric eq, room correction, etc) 20x faster than the time it takes to play that track. If this number is greater than 2x, your cpu has sufficient power.
The higher the processing speed, the lower the cpu load, and hence the lower the fan speed, so higher is probably better. 20x (i.e. ~5% cpu load) is plenty fast.