@dwanthny - Deleted & cleared my iBooks library on my iPad then went through this from your link (
https://www.mobileread.com/forums/showthread.php?t=85856 ) 1117 books transferred to iTunes in 78m 57s then it took 34m to transfer to my iPad...
After deleting tags & after conversion from mobi>ePub, tags do not show in the Tag Column or Tag Browser, the way I want it but if I open the converted book(ePub) in Calibre viewer it is shown on the second page below the Title & Author and above the book summary...
I have this ticked Preferences>Conversion>Common Options>Structure Detection>Insert Metadata as page at start of book - As I want the book summary in the metadata...
Have tried reconverting the books that are still showing tags but can't get rid of them...