Ultradisc Versions of War, Unforgetable Fire, The Joshua Tree

This might have been covered before, but I was wondering what exactly are
the differences in the original cd releases of War, UF, and JT as compared
to the Gold Disc versions from Mobile Fidelity. Obviously they are supposed
to sound better, but is it really noticeable? Also, I've heard that the
Gold Disc versions of some of the tracks are longer? Can anyone confirm
this? What exactly has been added?

Thanks,
John

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