Sauron Greater than Morgoth...

[Raynor]

Originally Posted by Gorthaur the Cruel

Also, Gandalf said something in the council that if Sauron were to recover the Ring, his victory would be so absolute that Arda would be subject to a second darkness.

Hm, I believe you are rather referring to the last debate:

Originally Posted by The Last Debate, RotK

Concerning this thing, my lords, you now all know enough for the understanding of our plight, and of Sauron's. If he regains it, your valour is vain, and his victory will be swift and complete: so complete that none can foresee the end of it while this world lasts.

Originally Posted by Gorthaur the Cruel

And would Sauron -- if the Ring was recovered -- be a great threat to the Lords of the West?

What lords do you have in mind? If you are talking those of M-E, then yes, as seen from above; if you are talking about Aman & co, I really don't think so, as there is no evidence he was ever a match for them. He actually dreamt that the valar & co forgot about the whole Arda thing; such wishful thinking would not be called for if he considered himself up to the task of confronting them.

Originally Posted by Gorthaur the Cruel

And with the Ring, was he mightier than Eonwe (Manwe's maia general)?

"Objection, your honor; calls for speculation!"

I doubt that.