gis-distance | Calculate geographic distances using latitude and longitude | Map library

My previous question discovered that the cause of my performance troubles is because using the indexed distance operator in Postgis is very slow on large areas that return many rows.

As a result, it seems the ideal solution may be to pick some arbitrary miles distance amount and then use the indexed distance operator (ST_DWithin) when it's in that range (let's say, below 75 miles), and then to use the non-indexed distance operator (<->) when it's above that range (so, 75 miles or above)

My current function looks like this: