You are wrong with the Mb -> MB.
it's about 8Mb to 1 MB.
https://www.lifewire.com/what-is-a-megabit-2483412
As for when you download files online, everything is quoted in MB (megabyte) from file size to download speed.
That is different to Mb (megabit) which is quoted when you are looking at ISPs advertising their speed.
As for the upload speed, typically the normal user won't upload much so they seriously limit the upload speed. I think the BT i had was seriously underwhelming which was why it was seriously hampering the usage when multiple users were on