I don't think anybody can answer that because most people don't have both products.
However, I assume, based on its name, that the Pro Silence is less noisy than the Pro Gold, and that must be the reason why it's more expensive. It is also a newer model because I've had the Pro Gold for 3 years, and I have never seen the Pro Silence before.
Anyway, if you want to save money, the Pro Gold is probably a good choice. It is silent enough even for sleeping, and it consumes very little energy. My electricity bills are the same as before I bought it.