www.notetab.com
does a search and replace very quickly and counts the number of times it replaces x with y ...... file size is limited only by the amount of ram in your machine. FREE download.
HTH's
EDIT...... on a side note.... this is one of the VERY few windows programs I ever BOUGHT the PRO version of. I highly recommend it to anyone who uses windows. The closest Linux counterpart is BlueFish. Try it, you'll like it.....especially if you like the speed of notepad. NoteTab is FAST