I've examined the waveforms on mine, and the sinewave is very good, with a tiny 0.7% THD (mostly 2nd harmonic), while the strongest non-harmonic aliasing spike (around 3.1kHz) is around 60dB lower than the fundamental.
Yes, the sawtooth and pulse aren't quite their classic mathematical shapes (like various other synths), but are fairly close, and rolling off the top end of the filter makes the waveform look slightly better if you're into that sort of thing.
Meanwhile background noise is 80dB below peak level when no notes are playing.
By the way, I see absolutely no 11kHz spike on mine - and as mentioned above, this 3.1kHz spike is inaudible to me when notes are playing.
EDIT: 11kHz spike has since put in an appearance on some programs, but at a very low 85dB below peak note levels
I consider all these very good results, and am quite happy with the fidelity of my P12.
Martin