What is the difference between the STM32F411 and the STM32F722RET6 processors in flight controllers? What are the advantages of having the F7 processor over the F4 processor?
There are a few differences:
Firstly, the F7 chip used in F7 flight controllers operates at a much higher frequency, so can handle more operations per second.
This is useful when you want to start adding lots of dynamic filters, for example RPM filtering, alongside features such as antigravity.
Whilst an F4 can handle almost anything you will want to throw at it in this respect, it will not be able to do so forever (the F3 used to be standard but is now lacking features). Therefore, F7 is better for future proofing.
F7 flight controllers also have extra UARTs. This can be very useful if you want lots of extra features, for example SmartPort telemetry, Smart Audio, GPS and camera control. However, it is not the end of the world if you don’t have as many UARTs as you want as you can use softserial to add software UARTs to your FC. Of course, this also takes up processing power so an F7 may cope better.
Finally, F7 flight controllers have built in inverters on their UART ports, while F4's do not. So an F7 FC can handle any inverted signal "as is" on any of its numerous UARTs, while F4 flight controllers have a dedicated external inverter chip on the PCB connected to one of the UARTs.
Because of that, F7's make it easier to use UARTs for SBUS or other inverted signals as it means you can hook them up anywhere without any inversion mods, while on an F4 controller you can only use the special inverted pads (of which there is usually only one, labeled "SBUS").
The short answer is that F7 is faster than F4, mainly because the F7 can execute two instructions simultaneously. At 216 MHz clockspeed, the STM32F722RE series you asked about has more than double the frequency of the STM32F411 series.
What might matter the most apart from the speed when it comes to flight controllers is UARTs; the STM32F411 has 3 of them, and they can't handle inverted signals. The STM32F722RE has 4, that can handle inverted signals