I should mention - my husband is worried that the Snowfall White will look green covering such a large area

Thank you so much! I've read many of your comments on other threads, and I find your advice so helpful!

Lori is right White is a great choice. I also like Super White with Steam, but of course individual mileage may vary...lol

Thank you! I see Snowfall White as creamier, prettier than OC-151 which I find a bit dull and chalky, but I don't trust myself on such an expansive space. (With 20' high walls, I can't risk wishing I could repaint). My husband and I never agreed on the colors of that striped dress that was all over the web a while back, so no surprise we see these whites differently too :)

I also like Super White

That's a good one too.

I see Snowfall White as creamier, prettier than OC-151 which I find a bit dull and chalky,

Are you looking at in real life chips or swatches online?

Also, sheen will make a difference in how it looks.

The painter put eggshell samples of several colors I considered up on the walls, about 1' squares, wall onto trim: White, Cloud White, Steam, Snowfall White, Dove White, Chantilly Lace. Steam looks great as a wall color, a bright, beige-ish white. The problem is the trim. The paneled center hall is 2 stories high (20') and includes the entire hallway of the upper level. The painter recommends painting this whole space, from crown molding on the 2nd floor down to baseboards on the first floor, with my trim paint. The salesperson at the paint store told me to be careful about going too bright (she specifically warned about Chantilly Lace). I'm attaching a picture of a similar space (not mine). I love the color in this picture, but I have no idea what it is.