Did you try it out with movies and see how it looked? I still have a small low lumen 800x600 pj in my office and it's watchable at about 8' away and further. But I'm only watching a 65-70" picture.
I'm no expert here, but what you find acceptable would partially hinge on how far back you'll be sitting from the screen and how large the image will be. Obviously, the lower the resolution, the further back you'll want to sit, at least in my limited experience.