Assuming all adjustments are made with optics rather than electronics, then projecting onto a smaller screen would give you better results in a lit room.

Throw ratio is constant for any fixed lens, so reducing screen size also reduces throw distance.OTH, if the projector has a zoom lens, then the throw distance can be constant while the throw ratio is varied by adjusting zoom. With either lens, lumens are constant, so concentrating the image on a smaller screen increases intensity. My Dwin projects onto a monster 120 inch screen, and can only be viewed in total darkness. If I reduced the screen to a still-generous 80 inches, it would probably be good in dim light. But then I would have to move the projector closer to the screen or switch lenses.

The measurement you're interested in is "lux", which is lumens per square meter. For any given projector, reducing screen size brightens the image, because lux increases. With a 5000 lumen projector and a 100 inch screen, I would expect that anything short of direct sunlight would still be acceptable for viewing. Of course, there's a tradeoff between ambient light and picture quality that's going to be personal. So you should try to find a setup you can see in person.