I just installed Raspbian Buster to run some performance tests of my own software on my new Pi 4. To my surprise, the performance was nearly identical to that of my older Pi 3 (not even a 3+). So, I put the Buster MicroSD card into my old Pi 3, and it turned out that CPU load of my software doubled compared to what I had been before - the boot screen says "Raspbian 2.1 2017", uname -a "4.9.59-v7+".
I made sure that I am using the same binaries of my software, and the same settings file. The software is computationally heavy, and uses a lot of float calculations, some of them using NEON code.
Oddly, I also had a question from a customer about a week ago who had similar performance issues with Raspbian Stretch - I've sent him a copy of my old image and his performance problems were gone.
vcgencmd get_throttled returns 0x0 in both images.
vcgencmd get_config arm_freq returns 1200 for the Pi 3, 1500 for the Pi 4.
What can this be?
As a side note: Since I can run the Buster image on both Pi's, I have been able to get some performance values using Buster, and that shows a 2.2 time reduction in CPU load on the Pi 4, which looks really good - if I can fix the OS image. I have not yet tested other images such as Ubuntu Mate etc.