MOS capacitors, especially at low Vgs, have very poor series
resistance (channel R and gate R is in series with C).
But you want to have a look at how little R you can stand,
a super high quality capacitor may resonate with supply
bondwire L. A little bit of R may be quieter internally than
none, especially if your resonant decoupling f just happens
to be near a significant clock frequency or f/2 (the IDD
spikes happen on every edge). Supply ringing phase-in,
phase-out can create strange jitter behaviors and so on.