You can use Power Custom Fields PRO for huge data sets. Still, showing all the options, without being able to select them by name can be a torture. So, you can limit the value count and filter them by name selecting the ones which contain those characters.
In order to do this, you can use argv["query"] only if you set the Filtering Strategy (from Autocomplete settings) to Datasource.
Video
The following example shows the routine:
Script details
The script used in the video is represented below:
string [] issues = selectIssues("created < now()"); string [] res; for (string iss in issues) { if (contains(iss.summary, argv["query"])) { res = addElementIfNotExist(res, iss); } } return res;