One of the advertised key selling points of Drupal 8 is speed. But according to some numbers it seems like the Drupal 7 is actually quite a bit faster than the latest iteration:
This probably ties into the large architectural changes in Drupal 8 to that aim to modernise the legacy application. Of course perceived speed is what matters in the end, but with advertising being that Drupal 8 is faster than Drupal 7, I would suggest everyone to look into these benchmarks: Drupal 7 vs. Drupal 8 benchmarks
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This is what I have seen also on my server. Drupal 8 is 3 times slower than Drupal 7 for authenticated users. So Drupal 8 is not a good solution for medium-large scale authenticated web services.