Bono and the band wearing suits? The pilots can't fully operate a complex cockpit like the U2 with their suits inflated....too bulky, so my understanding is that they only are pressurized if the cockpit seal is compromised.

It's not the relative PO2/PaO2 alveolar-arterial ratio that's key, it's the minimum absolute alveolar PO2 value (~14kPa) that is necessary to keep us alive. Even an adequate PO2/PaO2 gradient that allows efficient O2 diffusion won't be sufficient if that value is much lower.