Illustrator CS 5.5 has memory issues when I create "distressed" looking art.

I work in a screen printing company and we often get requests for art work with a "distressed" look. I usually creat the art work and fake a distressed look with a grunge brush that I expand and unite with the pathfinder tool. I then color it to the substrate color, or white for creating seperations. The "negative space" becomes individual paths that cause lagging on my computer.

We recently upgraded to a computer w/ 64bit processor w/ 8 GB of Ram (though even on the old computer, we had the same issue).

My issue lies in that when I create multiple versions of this art. I get a warning about lack of available memory (which we should have plenty, as this when I save the files it takes significantly longer than other artwork). I have adjusted the scratch disk settings to work of an external drive. But when I make too many copies (which I have to do for the sepperation process) a warning window shows up that says:

"Can't Finish previewing. Could not repeat the requested operation."

and it switches to a wireframe preview. Then if I try to save, it says "An unknown error has occured."

I've attached images to illustrate this problem. I had to do quite a few more copies of the art to illustrate the point, but significant resources are lost and I am usually unable to save my work when this happens. I often have to do color seperations, so this requires multiple versions of the same art. I've lost many hours on this "bug".

Is there any tips, resources or anything available that you can let me know so this stops happening. Distressed logos are in style, and I can't tell my employers that I can't do them when they bought a new computer to handle the limitaions of the old one. This same thing has happend on both the old computer and the new one.

Image may be NSFW.
Clik here to view.