You now have a ~15-20 MB FLAC file that is, for all portable and casual listening purposes, audibly identical to a CD. This is the best yt flac you can achieve.
YouTube does not actually host audio in FLAC. The "best" quality you can get from a standard YouTube video is typically 256kbps AAC container) or at a similar bitrate. No "Upscaling": Converting a 256kbps YouTube stream to FLAC will improve the sound quality to "studio level". Prevention of Generation Loss: The main benefit of choosing FLAC is that it is a lossless container
Here's how each contender fared in my testing:
Open the resulting .flac file in Spek. You will see: