OK, so I've just been using Firefox to navigate to the download site and save it.
Used your WGet for windows and I still do not get the same checksum and extraction with 7Zip is still corrupted data. Byte count is correct.
Kinda puzzled. Downloading isn't really that hard to do. Downloaded and burned a stock RPi image with no problems.
So, just to see what would happen, I broke out the toughbook and threw in the Linux Mint cage. Wget in that and Bob's your uncle, correct byte count, md5sum, and extraction works.
Strangely, download rate on that was only half what it was in the windows box. Dunno if that could be related, it was kinda slow either way.