One gold key is worth about six silver keys. That means that you should never buy silver keys with gems because the math doesn't work. They are 60 gems each and six times 60 is more than 300 gems for a gold key.
Gold keys have a 45%/45%/10% Great/Rare/Epic chance per chest and a guaranteed epic every 10 keys without an epic. Or, as we call them, Pity Rolls.
This calculation is also important for knowing the most valuable gear for farming.
The noble boots and the chest give you both a 5% increase in gold keys, making them incredibly valuable. And even though the noble ring gives you a 15% increase in silver keys, it's only half as good as the 5% increase in gold keys.
