It's FileSeek v6.7 installed on one of my old PC, so I cannot use latest version. However, the search performance is MUCH MUCH slower than GrepWin bundled in Notepad3 which is a modified version of https://github.com/stefankueng/grepWin.

From process explorer, it looks like GrepWin uses 8 search threads but FileSeek uses much less threads. Is it possible to specify the search threads to improve performance?