We do not know what the future monetary system will look like.

Historically, it is bimetal standard and occationaly rotates between gold and silver. 

What is the future monetary standard? I think it will be a basket of commodities. Gold is just one of component and silver is the other, plus oil, plus copper, etc.

So Central bank buying has one key driver, the concentrated wealth of gold. Silver is bulky, and cost of safe keeping is an issue. It does not mean silver is not on their target. We just do not know. China has large reserve of silver mine. So it is not buying. But that is not to say it wont be a monetary component.

Remember, IMF's definition of monetary metals are, gold, silver, platinum and paladium.

We can wait and see in five years which performs best. My bets are that silver will do much better than gold. When panic hits, there will be bigger demand for silver than gold when price is high.

By the way, I own all of those metals. :)

p.s. silver is suppressed by JPM on paper trading. Actual demand surpass supply.