Hi Miles,
C0G have both lower voltage coefficient as well as the temperature coefficient. The dielectric is another consideration. Depending on the capacitor, there can be a large change in the value of capacitance as more voltage is applied across it. Also the lower grade caps can be noisy due to the dielectric.
Mica, film type caps, and MLCC C0G are the best (in that order) but the first two are often much larger physically for the value of capacitance. I have used X7R, but the best results are with C0G. You will have to experiment with X5R to see if it will meet your requirements as I don't know of a C0G that high in value.
Best regards,
Bob B