[nina foresti]

You asked about Tebaldi's voice.
She had a powerful spinto sound and a beautiful one. Callas admitted she wished her sound was like Tebaldi's. And even Bing dubbed her, "the voice of an angel."
OTOH: Tebaldi always seemed to have a slight problem getting up there to the high note and sometimes just rested a tad beneath it. Her acting too left a lot to be desired except for, ironically, near the end of her run when she gave forth with an incredible performance of Minnie in "La Fanciulla del West" in the famous Poker scene. Her "tre assi e un paio" line was a shattering and stupendous tour de force like nothing ever heard before. The audience went wild!

 

[nina foresti]

I believe earlier in the thread someone compared Tebaldi's fach with Callas' and said that Tebaldi was a lyric soprano. I have always considered her a spinto soprano and Callas a soprano sfogato -- a rare voice that effected a mezzo sound up to a coloratura sound.
Tebaldi had a lot of power and Millo came close in that department.
Today, Sondra Radvanovsky probably has the most power of today's crop of sopranos.