I need to run some 1206 ceramic caps at 55 volts or so, as bypasses, and I have a 4.7U 50V part in stock.
Capacitance drops to 0.42 uF at 50 volts, where leakage is about 100 nA. At 200 volts, it's 250 nA, and at 300 it's 1.5 uA. I have a couple soaking at 300 volts.
Looks OK to me.