B747-400 with RR engines could make FL451, although I only did it once, just to see what it was like. Very high, quiet (due to low IAS) and dark blue, as it turned out. Quite regularly achieved FL410 at the end of the flight, but FL390/400 was more normal.
B787-8 and-9 could make FL430 and we achieved that reasonably often. One remarkable memory I have at lower levels is taking off my headset and hearing the whoosh of opposite direction traffic as they passed 1000ft above or below. Even at M0.85, the flight deck was very quiet.