PWM/DC-Motor Control: Pins 5 and 6 (sounding) slightly slower?

Hello,
I'm using the Arduino's PWM pins for controlling a brushed DC-motor with a L293D H-Bridge driver. When using PWM pins 5 and 6 the motor runs slightly slower than if either one of the other pins where being used (at least of what I can notice from hearing).

According to this TimerPWMCheatsheet pins 5 and 6, the slower ones, are driven by Timer 0, the others by Timer 1 and 2. Timer 1 has a smaller duty cyle of only 256, compared to 510 of the others. It also runs on a higher frequency of 976.5625 Hz instead of 490.20 Hz. Is the difference in these parameters the reason for the motors behavior? And if so, why?

Thanks for your help!

https://www.arduino.cc/reference/en/language/functions/analog-io/analogwrite/
section “Notes and Warnings”