I think you probably want to take pictures that would point out differences in the projectors, and that everyone has easy access to.
Also remember it's very hard to compare screen shots. Someone may have a crap camera but a superior image and nobody would ever know! Also their setup may stink (ambient light, screen too large, projector too close/far, crap cables, etc.). I.e. if you take the same PJ and project from 10 ft instead of 20, you'll get a brighter image at a sacrifice of CR.
Black level, contrast ratio, lumens at D65, color accuracy, detail/sharpness...how are we going to compare all of these?
Not wanting to be a stickler or drama queen about it, but it will be very difficult I think. I'm sure I could go run over to the G90 stack or Art's HT5000 and take you a complete crap picture that wouldn't represent their setup at all. =D