Never underestimate the feasability of overdriving VCO Vtune. Check your datasheet of course, but to cover there own asses component manufactuers always give lower and upper headroom in addition to AMR's.

Stability of feedback circuits is generally quantified as phase margin, a function of the phase of the system loop gain evaluated at the frequency where loop gain magnitude goes to one. Introductory analysis uses ideal blocks having low output impedance and uni-direction signal transmission where finding loop gain is relatively straight forward. Real systems have real elemen...