High frequency filtering in audio output

One thing that I've put off for a long time is selecting filter caps for various op amp output drivers. 

Today I had a look at some datasheets to figure out what others are doing. 

Generally, it seems that filtering (by putting a cap in parallell with the feedback resistor in an inverting op amp) is only done at the last stage of the circuit, not within the circuit itself. It seems that very little filtering is done except for biasing using electrolytics in the audio path to center the signal. I assume the final filtering is just to stop radio frequencies, stuff that we don't want to escape the circuit perhaps?

Here is what I found

Self on audio (book) page 237: 100pF/4k7 = 339kHz

Self on audio (book) page 359: 27pF/10k = 589kHz

JP8 source mix: 10p/100k = 159kHz

JP8 VCA cont 15p/100k = 106kHz

Juno 6 out: 47p/3k3 = 1.02MHz - See juno 60 where the 3k3 is actually crossed out in the schematics and 27k written instead.

Juno 60 out: 47p/27k = 125kHz

Juno 106 out: 22p/33k = 219kHz - Interestingly enough, and supporting of my theory that filtering only happens at the last stage, the 106 has the same feedback resistor as the Juno 6 (3k3) right after the filter, but no cap, as it has a mixer at a later stage too, mixing in High-pass filter.

JX-3P out: 330p/10k = 48kHz

JX-8P synth mix: 100p/47k = 33.8kHz

JX-8P chorus: 100p/22k = 72kHz

THAT4301 reference: 47p/20k = 169kHz

Sooo, I can't say that the findings are exactly conclusive. Before starting this research I suspected that the cutoff would at very least be above 22kHz (being the upper limit of human hearing) and perhaps at least the double as we want to make sure to not remove anything wanted. Most of these results seem to support that, with roland ranging from 33kHz up to 219kHz (disregarding the Juno 6 which seems to be too high). I'd say somewhere between 100 and 150kHz is probably a nice compromise.

Now, I started looking at this to find a good cap for my distortion circuit, which has an output feedback resistor of 120k. Playing around with various caps and looking at the output of the scope, it seemed like 10p would give a result where frequencies up to 22kHz did not get much attenuated. Calculating the cutoff using 120k/10p gives 133kHz which incidentally fits nicely between 100k and 150k.

That said, as the distortion is in the middle of the circuit, I may as well skip filtering alltogether.