Sorry, I made a slight goof with the last plot as the trace for the poly 470pF cap was from the wrong S1p file. To make the traces overlay correctly I have to make sure that both VNAs have the same start and stop frequencies and both have 101 points and the same applies for the simulator that plots the results. Otherwise the graphing engine creates interpolation errors and the trace will look incorrect. I've corrected this for the poly 470pF cap trace. As a bonus see the yellowish trace in the plot below. This is probably the highest Q cap I can find at about 470pF. It is a pair of 1111 series 820pF ceramic caps in series to make up a 410pF cap with very high Q. In terms of highest Q across the HF bands (for approx 400-470pF) it does seem to be the daddy at the moment...
Obviously, I had to measure this with the Agilent VNA and I'm not sure how realistic this result is for the 820pF in series with 820pF. I would definitely treat this impressive Q result as 'educational' rather than accurate!
