I disagree that only a limited amount of gold exists and that that's why it is protected from inflation. Who knows how many places which are still unexplored could contain gold. Cash is out of the question in that regard. So Bitcoin is the best like you said. 
yes that is fact that no one know that how much gold still can be explore, and no one know the present amount of gold that how much gold is present int this world, as gold is too much stable and there is a little fluctuation in the price of bitcoin, where cash is limited and centralize currency, therefore to me the best option is bitcoin which is decentralize a universal currency which can be use equally in all over the world. but the user of bitcoin are still very low still hope that a time will come when all the people of the world will be using bitcoin.