Variable Frequency PWM to Analog Circuit?
What you want is not possible.  You now say that the PWM frequency can vary from 5 Hz to 500 Hz (200 to 2 ms), but that you want the filtered result to settle within 5% in 5 ms.

Think about it.  How is the output supposed to settle to the average value within 2.5% of the pulse period?  Until the pulse is over, how can you possibly tell what it's on-fraction is.  Unless all your pulses are on for less than 5 ms, there is no way to extract the information from each pulse that fast.