Just checking through my nodes. Found an answer to this some time ago, and thought I would post a response for anyone who stumbles into the same situation:

The bottleneck would appear to be the TIF image compression. If you disable compression in the following manner:

$success = $img->write(filename=>$path, compression=>'None');
[download]

the program screams. Of course, as the purpose of my script is to save space, this isn't optimal ;)

The compression functionality may work faster on a *nix platform, which is unfortunately not an option for what I'm doing here. As such I have done no testing to either prove or disprove this. So you may wish to take this with a grain (if not a pound) of salt if attempting this on *nix.

Good luck!
MrCromeDome