It totally depends on the content of what you're projecting. 600:1 will actually do a failry decent job for most computer-based content. I used a projector for years with a 300:1 contrast ratio for watching DVD's and was fairly happy with it, although I felt the black level was higher than I would've liked for those dark scenes. But it wasn't horrible, and if you're not worried about photo images looking like they're in a movie theater, it won't matter much at all. Nobody will even notice it for Powerpoint presentations and the like.

Lumens are a different story. Since it's a measure of brightness, it's a big factor, especially when you're trying to use the PJ in an environment where you don't have complete control of the lighting. Ambient light quickly makes your image look washed out, especially if your projector has low brightness to begin with.

"Beauty" and screen image including effect of contrast ratio is very subjective and varies from person to person.

In our home we have pretty well matched our "business" projector with the right screen with both placed in a room well set up for Home Theater so, to us and our neighbors and friends that have watched movies it is simply outstanding with a contrast ratio rated at 350:1.

Frankly, movie viewing with it compared to a few of the "home theater" labeled PJs we have seen it very much holds its' own projecting a great image with very good flesh tones and detail in dark scenes with an image approx. 50 in high by 80 in wide with 86 i diagonal in 16:9 mode and almost 60 by 80 by 100 in in 4:3 mode.

So our experience is that if you have a "business" environment for computer graphics with ambient light or if you can create a true theater environment with dark walls and ceiling and complete light control either way you should create a good viewing experience.