A self-sustained Radiation-Pressure driven MEMS ring OptoMechanical Oscillator (RP-OMO) attaining an anchor-loss-limited mechanical Q-factor of 10,400 in vacuum has posted a best-to-date phase noise of -102 dBc/Hz at a 1 kHz offset from a 74 MHz carrier, more than 15 dB better than the best previously published mark [1]. While enhanced optical and mechanical Q both serve to lower the optical threshold power required to obtain oscillation, it is the mechanical Q that ends up having the strongest impact on phase noise [2], much as in a traditional MEMS-based oscillator [3]. This motivates a focus on increased mechanical Q-a challenge in previous such devices measured in air-and requires measurement in the absence of gas-damping using a custom optical vacuum measurement system. The improved phase noise performance of these RP-OMOs is now on par with many conventional MEMS-based oscillators and is sufficient for the targeted chip-scale atomic clock application.