The Balrog vs The Witch King

Nevermind the Balrog vs the Witch King. What of the Balrog versus Sauron? The victor of this duel would surely overcome the Witch King. Both were servants of Morgoth, neither were directly in league with one another, however, and they certainly were not allies in The Third Age.

According to Legolas, Sauron would be the favourite:-

It was a Balrog of Morgoth. Of all elf-banes the most deadly, save the One who sits in the Dark Tower.

But how could Legolas know this? Who has ever trialled their strength at both the Balrog and Sauron?