It depends on what you want to shoot.
"People in a room/ across a room" doesn't tell me at all what you are aiming at.
If you just want to get the images, you can use any longer range lens to just get their picture.
But if you are aiming for character, intimacy, for more portrait style work, I wouldn't go with too long a lens, as it flattens the face, takes personality out of it.
In lesser movie productions you see the camera man use a lot of long lenses, because it is easier that way to get a symmetry into the image. Great camera men get great shots with shorter lenses.
Regarding that comment about the "stupid idea" to use a "normal lens" for portrait: it depends on who's doing the shooting. As Pierre Assouline mentions in his book "L'Oeil du siecle", Cartier-Bresson used almost exclusively a 50mm lens, also for his portraits. If someone here knows better than Cartier-Bresson, he should scan his images for protruding noses. Be assured, you won't find any.
I would rather shoot a portrait with a 50mm lens (35mm in digital), than with a 300mm lens (200mm on a digital). I guess calling someone stupid, and then shoot portraits with a long range cannon is a double insult, first of the person insulted, then reason insulted.
I am always astonished how easily people throw worthless adjectives at others in internet forums. Do they really think it makes them look superior? (and their words always come back at them like a boomerang).
Intimacy:
In a portrait you need the sense of being close to the person, close in the sense of intimacy. You can't get that feel when you are looking at someone like through a sniper rifle visor.
For 35mm 80 to 85mm is excellent. (Some people liked 90mm, or even 100mm lenses, but that's where it stops. A 135mm lens is not a portrait lens any more).
For a DX sensor 55mm is ideal.