I actually had begun acquiring some "data" on this very topic a while back...
Here are the scramble screens for Wes', Chris', and my basements' cab.
In the final picture, I compared my "rug" against Chris' and against the (inverted*) mame scramble screen, this was when I was attempting to determine the overall "patterns" of the screen; ie. banding, sprite vs. text regions and specific distribuitions of color.
Such Nerdery
* I noticed that the mame "rug" is displayed on screen "vertically inverted" when compared to the arcade hardware, IMO it's a funny (yet understandable
) oversight on behalf of mameDev