This is something that has cropped up a few times now, particularly on bigger sites. There is a common misconception that if you combine a text search with a template or within folder search, it will limit the scope of the text search and speed the search up but this is not the case. If a relatively common phrase is used in the text search, it will search the text catalogue for that phrase and then apply an additional filter based on the specified template/within folder criteria.

In a recent example we had a client with a text catalogue over 150GB and when using a fairly unique phrase it performs well, with or without any additional filters. However, if they use a common search term but "filter" it using quite specific field criteria it still takes a very long time to return the results, in some cases nearly 10 minutes (compared to 2-3 seconds for more unique phrases).

I appreciate there may be some scope to improve performance using hardware/resource or other settings but they won't bring about a dramatic change to bring the speed inline with user expectations (as we're all used to Google nowadays!) I know this would require a major architecture change but just putting it out there.