Remember that caps have a tolerance. So the 4n7 aka 4700pf with a %10 tolerance can actually be between 5170pf (5n17) and 4230pf (4n23). This will allow you to not sweat the small stuff I hope. I still order and put in the "prescibed" value though hahahaha.
again, your 20pf cap could be anywhere between 18-22pf. So I would go ahead and use it for C5.