I’ve never gotten my 69’ Twin Reverb with D120Fs to break up. I’ve never lasted more than a few notes with the volume on 10 though. I have a Carvin x100b that I’ve never heard the clean side break up. I usually either run into a pair of EVM12Ls or Mesa C-90s. The X100b is actually surprisingly similar sounding to my TR if set right, just a bit more compressed sounding. If you put a 5751 in the PI it’s even closer (the 5751 phase inverter seems to lessen the compressed tone a bit).