proceed with caution:
1. given simple stb analysis (iprobe/cmdmprobe), not sure why the author prefer voltage mode open loop gain to check stability;
2. the common mode stability check is questionable at the breaking point
3. distortion will be much easier to sim in spectreRF through harmonic balance (flexbalance) for weakly nonlinear or shooting method for strongly nonlinear. Transient response is not as reliable.