Use the lightest shade of the color you like, you will be amazed at how it looks dark on that big wall. Try painting the entire wall for a more dramatic effect.

I would definitely paint the entire wall, including both sides of the fireplace and then into the kitchen.

I've recently used Benjamin Moore's Horizon in my home office, and it looks wonderful especially beside the white bookcases. Stonington is also nice, but definitely darker. I don't think they would look silver, but make sure to use a flat or almost flat.

We are painting a lot of our walls different grays (it's so frustrating not to be able to use the phrase "shades of gray" anymore.) I highly, highly, HIGHLY recommend getting any and all of the ones you are considering in sample size first. One of the colors we choose looks completely different in the living room and the bedroom. Those little cards are not a good representative of what grays will look like in your room. One sample we bought of a pretty gray ended up looking like dirty water on the walls. It's so worth the 3 bucks a sample.

That being said, we are going to paint the living room Stonington and it looks great. But it does have some browning undertones, at least in our lighting.

Hope this helps!

Thank you so much for all the advice we are excited to get our project started. cheers!