Ah, I see.
I can't say that I noticed that issue on either the Z90 or X1, and they're both 800 x 600, and really only a demo will tell you if the image is ok to you..
Have you seen a DLP before? Rainbows can be an issue, so to be sure that you're not one of the few that see them, you should try to see one in action.
The X1 has a slower colour wheel, so may be more prone to them, but may be a better bet as it's a cheaper machine. You won't have spent so much then...
What about selling it on if you bought either and didn't like it? Could you do that?
Gary.