How (much) does FFT speed up a SA?

[RBBVNL9]

Modern spectrum analyzers often add FTC analysis to their traditional swept-tuned designs in order to speed up speeds at low RBW settings. How much does FFT help in this respect? I tried to answer that question for my Rohde & Schwarz FPC1500. In the attached overview, you find the results.

If you are interested in how I carried out these tests, check out the video at https://youtu.be/W9Q77xTSRrA