I like your picks and add these. I tried to stay away from anything too new, since I'm not sure how old a song would need to be to be considered a 'classic' or a 'greatest' love song. I too, had picked Stand By Your Man for, Kellie.
Paris - Saving All My Love For You
Taylor - When A Man Loves A Woman
Chris - Nights In White Satin
Elliot - Since I Fell For You
Katharine - At Last
Kellie - Stand By Your Man
Not bad suggestions except that Gideon did "When a Man Loves a Woman" earlier in the competition and it was great. It was voted the farewell song everyone wanted to hear again on the AI website. He may not want to be compared to someone who was voted off lest they get any ideas!