andrewbell, it all depends on the kind of images you make. Your gallery is empty so I can't judge if you'll need 8GB or not, so let me show you some of my images which would require very close to 8GB.

Look at the green areas in this one. Those are millions of trees.
http://www.renderosity.com/mod/gallery/index.php?image_id=1889407

Again in the next one, a huge number of trees and thousands of buildings. The mountains in the background are several terrains with 4096x4096.
http://www.renderosity.com/mod/gallery/index.php?image_id=1863411

Not as demanding as the previous ones, these two also have very dense ecosystems.
http://www.renderosity.com/mod/gallery/index.php?image_id=1849011
http://www.renderosity.com/mod/gallery/index.php?image_id=1763313

So, if you want to do similar scenes, I'd definitely recommend very close to 8GB.