Permanently deleting files on my Windows PC?

There are many programs implemented with the Gutmann method you've mentioned, especially by overwriting file patterns. If you only want to erase multiple files and not wipe the entire drive, use Eraser. Not sure if you already know this program, but it's essentially a file shredder. It is a freeware and open source security tool to completely remove certain data from HDD. It can overwrite data several times using randomised patterns of binary code.

Or, you can use Recuva to find any files that have already been supposedly deleted but still are recoverable, and then securely overwrite them. Be sure to set Recuva to a high number of passes for secure overwriting as well. It'll overwrite the portion of the hard drive where the file lives repeatedly until it "decreases" its chance of recoverability

Hope that gives you a bit of ideas