It is important to calculate the Q factor of the tank while designing an LC oscillator. It is one of the first few steps you should do before getting into the cross coupled pair design, as the quality factor largely determines the overall performance of the oscillator namely the phase noise, power consumption etc. The theoretical maxima for the FoM of an oscillator is given by FoM=174+20*log10(Q) dBc/Hz
You can pump an AC current (magnitude=1, phase=0) into the LC tank, and do a simple AC analysis and look at the maxima of the real part of the voltage developed across frequency. The magnitude of the maximum voltage developed is the effective parallel resistance of the LC tank and the frequency at which that happens is the resonance frequency. This is a simple AC analysis and you should be able to get the results quickly.