Using your formula, and the values of capacitor and resistor in the circuit. I get a value for frequency of 7796 Hz

But using the formula of *f* = (1.732) / (2πRC), I get a value of 5513 Hz. How is that?

Exalibur - your formula applies to another phase shift oscillator (1.732=SQRT(3).

More than that - please note that two basic versions of the phase shift oscillator exist:

1.) Three RC lowpass sections: wo=SQRT(6)/RC

2.) Three CR highpass sections: wo=1/[SQRT(6)*RC]

More than that, you should consider that in your circuit R4 loads the last RC section and, therefore, the oscillator frequency will slightly deviate from the ideal.

**EDIT:** The formula as given by you (factor 1.732) applies to the following phase shift oscillator :

Replace the last RC section and the inverting opamp stage by an active inverting integrator (classical Miller integrator). This has the advantage that the input resistance of the inverter does not load the last RC section.