Photoshop :: Applying Filters To High-resolution Images Has Poor Effect

When applying filters such as accented edges, ink outline, etc to a medium sized image (1024x768 or 1280x853) produce some pretty cool results.
 
However, when applying those same filters to larger images like files with a 5184x3456 resolution, the filters have little to no effect.  I'm guessing this is because there are so many more pixels that altering each pixel has a less noticeable effect.
 
You can see an example here with the accented edges filter run over a smaller version of a picture I took, and then a larger one (that was then downsized to make it viewable): [URL]
 
The 1280x853 one looks pretty cool.  On the larger 5184x3456 version the filter had almost no noticeable effect.
 
The problem is that I want the cool looking version like is seen in the 1280x853 version, but at a high enough resolution to print on a large canvas that is, say, 40' x 40' or so.  Is it possible to get the bigger image to look like the smaller one without losing the resolution required to print it on a canvas that large?  I've been trying to figure this out for weeks now...