In practice, you would not dream of descending that far.
Why on earth not? If it gives you a better specific fuel burn AND a better ground speed it is the place to be!!
I've flown SYD-MEL at FL 220 in a 737 before now, as it offed the best fuel burn and a lower flight time. Jets don't HAVE to fly in the 30s and 40s, they still WORK down lower!!