That's an interesting question. I'm tempted to say the mid-20th century, possibly symbolized by Neil Armstrong setting foot on the Moon. The Faustian worldview is about conquering nature and eventually spreading out into space. That probably represents the peak effort to achieve that, and some impressive stuff was indeed done. It's been all downhill from there, IMHO.

On the other hand, I think new inventions peaked in the 19th century, so perhaps sometime during that century was the real peak of Faustian civilization.