If you want to use a Windows application instead of a command-line utility, I use the free open-source utility Notepad++ to replace strings in huge text files. It made 15907 string replacements in MUCH less than a second in a 312 megabyte file. Notepad++ is not limited to text files.
Fwiw, I first tried the PowerShell approach, but Notepad++ was vastly faster and easier for my needs.