Has anyone tried the "paint on theater screen"?
I painted my screen. My projector is a Benq W6000. Like your optoma, it is a DLP and therefore suffers a bit when it comes to black levels. In my case, I also have some ambient light issues to deal with. The picture quality is excellent. Total cost was about $250 (including all of the paint that went into the mixture and the purchase of a pretty good HVLP paint sprayer unit). Prepping the wall was pretty easy (but is does require a pretty bright halogen lamp to ensure that you have made the wall truly smooth). Painting was much easier (and cleaner) than I had anticipated. I have a lot of experience with more traditional airless sprayers and was pleasantly surprised with how little of a mess the HVLP unit made.
If you are seriously interested in this option, go to the DIY screen forum over at avsforum.com. I swear there are people over there who must do nothing other than mix up screen paints and test them out all day long. If you create a post describing your situation, you will get some very prompt and specific responses from highly informed members.
edit: I should have added that my screen is 120" diagonal.