I think it's a bit optimistic to hope that a VNA could measure that component with a basic s11 measurement. I did a few quick sums and at 100kHz, a 485pF capacitor with ESR 0.58R, -3282R reactance, (Q of 5655) will have a reflection coefficient of something like mag 0.9999946. I did some tests on my nanoVNA a couple of days ago with a test load consisting of an ATC 100B 39pF porcelain cap in series with a 1R 1% 0805 SMD resistor.
The aim was to see how well it could measure the Q of this network across the 2-30MHz HF band. This cap will have a similar reactance magnitude as a typical handwound toroid using either Micrometals 2(red) or 6(yellow) material and this is why I chose these component values to put in series. Things generally get difficult for a modern VNA when the magnitude of the reflection coefficient creeps above about 0.998.
The plot below shows the theoretical Q curve in green for 1.02R in series with 39pF. The blue trace is for the Q measured with the nanoVNA and the Q was also measured with a lab VNA and this is the brown trace. The nanoVNA does OK until the Q goes above about 200 and then it gets very noisy. This is a plot taken with no averaging on the nanoVNA. I've improved my cal kit definitions since I took that plot so I'll try and find the RC network and measure it again. It isn't a perfect yardstick because the ESR of the 1R resistor will tend to creep up slightly with increasing frequency and the ATC cap probably has an ESR of 0.02R across the HF bands. However, I think it is a useful test.
