Yuri's port of Recoll is a search app that can create WPS objects with search results. Because it was ported, I don't think that it uses the slower WPS functions that work with WPS objects, too. (The slow WPS "Find Objects" uses them.) Features are impressive. The last time I'd tested this, it worked pretty well, but consumes some of the short lower shared memory. That was the reason, why i'd dropped it. The situation has changed with the new kernel and newer Mozilla and AOO apps with respect to higher memory.
DataSeeker, initially developed by Alessandro and now maintained by Andi, was developed with regard to fastest searching. Both apps are OSS. I'm using DataSeeker daily.
Keith' SearchPlus has features that DataSeeker lacks: Filter by date, search in .zip files and sortable output list. I haven't compared it with DataSeeker regarding search speed, because I noticed at some point that it's shareware. I also don't like one of its strange dialog that doesn't comply with usual PM rules, while I must admit that I haven't checked it since then, what was about 10 years ago.
I'm happy with DataSeeker, but would like to have the date option and eventually the sort option added.
I've just read a bit more about Recoll and it supports EA filtering and works with an index. The index should make it much faster than other search apps. It looks like I have to test it again.