Suggestion: When simply wanting to undelete a file on a good drive, Recuva just updates the MFT instead of re writing the whole recovered file.
Got to be worth a saving of time for large files, and also mucking around with a 2nd drive.
This would be very difficult technically, especially with large fragmented files, and with a lot of files phenomenally complex. There is no Windows API that allows for this, and the MFT is protected from any outside interference. It's a more stable process to recover to another drive, inspect, and copy back into place.